[Pw_forum] k-point

[bf azi]

Dear all

whether the number of k-points in final result of relax is effective?

[Pw_forum] k-point

[Seyed Mojtaba Rezaei Sani]

Dear Musari

Have a look at http://www.cryst.ehu.es/cryst/get_kvec.html

HTH

On Tue, Apr 26, 2011 at 12:54 PM, Abolore Musari  wrote:

> Dear QE User,
> I am having a problem as regard (k-point)
> I am working on monoclinic system, and am using xcrysden to get my k-point
> and my question is how do I know the special points (k-points) to select
>
> from the Brillion zone in the xcrysden k path selection?
>
> Thanks in anticipation of your favourable assistance
>
> Musari Abolore
> Dept Of Physics
> University of Agriculture, Abeokuta
> Nigeria
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 
==
Seyed Mojtaba Rezaei Sani
Computational Condensed Matter Research Lab
Physics Department, Isfahan University of Technology
84156-83111 Isfahan, Iran
Tel Lab: +98 311 391 3731 Fax Office: +98 311 391 3746
s.rezaeisani at ph.iut.ac.ir
===
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[Pw_forum] k-point

[Abolore Musari]

Dear QE User,
I am having a problem as regard (k-point)
I am working on monoclinic system, and am using xcrysden to get my k-point
and my question is how do I know the special points (k-points) to select
from the Brillion zone in the xcrysden k path selection?

Thanks in anticipation of your favourable assistance

Musari Abolore
Dept Of Physics
University of Agriculture, Abeokuta
Nigeria
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[Pw_forum] k-point

[Eduardo Ariel Menendez Proupin]

Abolore,I do not know any standard set of k-points for monoclinic system.
Chose the points that you think are representative, e.g, half of every
reciprocal lattice vectors, and path between them. I suggest you first
calculate the DOS, locate the points of the valence band maximum and
conduction band minimum, and be sure that they are in included in the
k-points path of the band diagram. Some maxima of the DOS are related to
lines were some bands are flat. Assure that these lines are included in the
path. A good method is to explain the DOS features with the band diagram. If
some feature cannot be explained with the band diagram, investigate the
reason.
It is like choosing 4 or 5 cities to visit in a tour by Italy, with a good
choice you will get some idea about the country and you can explain some of
the history from the monuments and museum, or the cafes that you visited.
As there is no convention for the letters that design the k-points in a
monoclinic crystal, PLEASE, indicate the coordinates of the points in the
figure caption or in the text.  [Pw_forum] k-point
*Abolore Musari* abmus007 at gmail.com

*Mon Apr 25 23:57:21 CEST 2011*

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--

Dear QE User,
I am having a problem as regard (k-point)
I am working on monoclinic system, and am using xcrysden to get my k-point
and my question is how do I know the special points (k-points) to select
from the Brillion zone in the xcrysden k path selection?

Thanks in anticipation of your favourable assistance

Musari Abolore
Dept Of Physics
University of Agriculture, Abeokuta
Nigeria
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-- 


Eduardo Menendez
Departamento de Fisica
Facultad de Ciencias
Universidad de Chile
Phone: (56)(2)9787439
URL: http://fisica.ciencias.uchile.cl/~emenendez
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[Pw_forum] k-point

[Abolore Musari]

Dear QE User,
I am having a problem as regard (k-point)
I am working on monoclinic system, and am using xcrysden to get my k-point
and my question is how do I know the special points (k-points) to select

from the Brillion zone in the xcrysden k path selection?

Thanks in anticipation of your favourable assistance

Musari Abolore
Dept Of Physics
University of Agriculture, Abeokuta
Nigeria
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[Pw_forum] k-point

[Rahen Badsha]

Dear All,
I am a new user of QE. I have a question.

What is meant by k-points in pwscf?


Regards,
Md. Rahen Badsha (Raihan)

A Post Graguate Thesis Student of Rajshahi University, Bangladesh.
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[Pw_forum] k-point

[Peter Wang]

k-points are used for integration over BZ which is described in any DFT book.

Yun-Peng

From: Rahen Badsha 
Sent: Tuesday, January 10, 2012 1:55 AM
To: pw_forum at pwscf.org 
Cc: pw_forum at pwscf.org 
Subject: [Pw_forum] k-point

Dear All,
I am a new user of QE. I have a question.

What is meant by k-points in pwscf?


Regards,
Md. Rahen Badsha (Raihan)

A Post Graguate Thesis Student of Rajshahi University, Bangladesh.




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[Pw_forum] k point selection.

[Li yan-ling]

Dear all users,

Now I'm learing to calculate the energy band or phonon dispersion by using
PWSCF code. For example 06, I got a different result by using Xcrysden
generating k points path (selecting the same high symmetry point as the
matdyn.in file in example 06). Now I want to know how to generate the
accurate k points path.

By the way, if one of you can help me generate a k point path about
hexagonal crystal with P63/mcc sacegroup(No. 194), it's my pleasure. I try
to get it myself, but fail to date.  If Ok, please email the k point file
to me.

Thanks in advance.

Yanling Li.

[Pw_forum] k point selection.

[Paolo Giannozzi]

On Mar 11, 2008, at 13:09 , Li yan-ling wrote:

> By the way, if one of you can help me generate a k point path about
> hexagonal crystal with P63/mcc sacegroup(No. 194), it's my pleasure.

the algorithm for automatic k-point generation is absolutely general.
You just have to specify how dense the grid should be along the
three axis (respecting symmetry, of course)

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

[Pw_forum] K-point parallelization

[Sergey Lisenkov]

 Dear PWscf authors,

  I am wondering does k-point parallelization work very well on any platform? I 
have noticed that on our cluster (IBM Blade PPC970 - power4+) PW code works 
slowly with k-point parallelization in respect to without k-point 
parallelization. Does it depend on the platform? 

  Thanks,
Sergey

[Pw_forum] K-point parallelization

[Axel Kohlmeyer]

On Sat, 26 Nov 2005, Sergey Lisenkov wrote:

SL> 
SL>  Dear PWscf authors,
SL> 

hi sergey,

SL>   I am wondering does k-point parallelization work very well on any
SL> platform? I have noticed that on our cluster (IBM Blade PPC970 -
SL> power4+) PW code works slowly with k-point parallelization in
SL> respect to without k-point parallelization. Does it depend on the
SL> platform?

you have to make sure, that you have a fast and preferably 
local scratch area available and use it. if you are using 
a networked scratch, your i/o load with increase immensely,
since each k-point 'pool' will write to the scratch concurrently.
on a networked scratch, especially over gigabit ethernet, this
will kill the performance.

axel.

p.s.: any news on the ru-potentials?

SL> 
SL>   Thanks,
SL> Sergey
SL> ___
SL> Pw_forum mailing list
SL> Pw_forum at pwscf.org
SL> http://www.democritos.it/mailman/listinfo/pw_forum
SL> 

-- 
===
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
===
If you make something idiot-proof, the universe creates a better idiot.

[Pw_forum] k-point-path

[Payam Norouzzadeh]

Dear QE users
I'd like to provide a list of proper k-points for my structure. How can I
generate them and what are the proper lines (or high symmetry points) in BZ?
Is there any tutorial or example to learn it?
Best regards,Payam Norouzzadeh
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[Pw_forum] k-point-path

[DENIS MAGERO]

Hallo payam. Im not sure whether I understood your question correctly
but incase you need the k point path for high symmetry points this is
what you should do;
Check on any paper that has dealt with your material and you can get
the points of high symmetry from there, probably the band structure
will give you the high symmetry points.
Xcrysden your structure and then at the top of your window select k
point path generation. You will have a window in which you can input
the high symmetry points you got from the paper by highlighting on the
structure you will have. When you are done, press done and select the
number of points you want generated. You can then save the points as
name.kpoint path.
About a tutorial, im not very sure, but there maybe.
If you need more clariffication jst email me.

On 21/06/2012, Payam Norouzzadeh  wrote:
> Dear QE users
> I'd like to provide a list of proper k-points for my structure. How can I
> generate them and what are the proper lines (or high symmetry points) in
> BZ?
> Is there any tutorial or example to learn it?
> Best regards,Payam Norouzzadeh
>


-- 
Dennis Magero,
M.Sc Student,
Computational group,
Chepkoilel University College, ELDORET
KENYA.

[Pw_forum] k-point-path

[Nandan Tandon]

Alternatively, you could use the
website:http://www.cryst.ehu.es/cryst/get_kvec.html
to get the coordinates of the high symmetry k-points.

Regards,

Nandan.

On Thu, Jun 21, 2012 at 6:31 AM, DENIS MAGERO  wrote:
> Hallo payam. Im not sure whether I understood your question correctly
> but incase you need the k point path for high symmetry points this is
> what you should do;
> Check on any paper that has dealt with your material and you can get
> the points of high symmetry from there, probably the band structure
> will give you the high symmetry points.
> Xcrysden your structure and then at the top of your window select k
> point path generation. You will have a window in which you can input
> the high symmetry points you got from the paper by highlighting on the
> structure you will have. When you are done, press done and select the
> number of points you want generated. You can then save the points as
> name.kpoint path.
> About a tutorial, im not very sure, but there maybe.
> If you need more clariffication jst email me.
>
> On 21/06/2012, Payam Norouzzadeh  wrote:
>> Dear QE users
>> I'd like to provide a list of proper k-points for my structure. How can I
>> generate them and what are the proper lines (or high symmetry points) in
>> BZ?
>> Is there any tutorial or example to learn it?
>> Best regards,Payam Norouzzadeh
>>
>
>
> --
> Dennis Magero,
> M.Sc Student,
> Computational group,
> Chepkoilel University College, ELDORET
> KENYA.
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum



-- 
***
Nandan Tandon
Department of Physics,
Worcester Polytechnic Institute,
100 Institute Road,
Worcester, MA
*

[Pw_forum] k point generation

[MMS]

Dear all,

I have been trying to understand the sampling of the Brillouin Zone for
integration in the k-space.  The method adopted in the automatic generation
scheme in Espresso is the Monkhorst-Pack one. I have been reading the file
kpoints.f90  in

espresso-5.0/PW/tools/

and I went through some of the forum archives
http://www.democritos.it/pipermail/pw_forum/2012-February/023321.html to
understand this.

I think the algorithm follows these lines

1. generate a shifted uniform grid in *crystal space* of *the reciprocal
lattice* and associating a weight of 1/(total no: of k points)
2. use symmetry of the reciprocal lattice to reduce the list
Here the weights of the eliminated points are accumulated
on to the remaining ones

This is what I was hoping to find
a) Some sort of check that ensures that k points fall within the
Wigner-Seitz Cell (first Brillouin Zone).
b) During the generation of the k point mesh, the sampling seems to not
extend in all quadrants of the crystal space, i.e., I am not able to find
negative crystal vectors. I expect them because the Brillouin zone extends
in all quadrants.

Can someone please explain this to me?

Regards
Meenakshi Sundaram M
Grad Student
Mechanical and Aerospace Engineering
Ithaca
Cornell
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[Pw_forum] k point generation

[giann...@democritos.it]

Quoting MMS :

> a) Some sort of check that ensures that k points fall within the
> Wigner-Seitz Cell (first Brillouin Zone).

> b) During the generation of the k point mesh, the sampling seems to not
> extend in all quadrants of the crystal space

it doesn't matter which k-point in the star we take as representative
of the entire star (with weight proportional to the no. of k-points in 
the star). k and k+G are equivalent. Also note that k and -k are
equivalent (by time reversal symmetry)

Paolo



This message was sent using IMP, the Internet Messaging Program.

[Pw_forum] k point generation

[MMS]

>
> it doesn't matter which k-point in the star we take as representative
> of the entire star (with weight proportional to the no. of k-points in the
> star). k and k+G are equivalent. Also note that k and -k are
> equivalent (by time reversal symmetry)
>
> Paolo
>
>
> Oh I get it!! Thank you very much. Just to summarize it,

It is enough to work in the unit cell prescribed by the reciprocal lattice
vectors and generate the k-points there.

regards
Meenakshi Sundaram M
Grad Student
Mechanical and Aerospace Engineering
Ithaca
Cornell
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[Pw_forum] k point value

[Padmaja Patnaik]

Dear all
I am using QE since last few yeras but still could not answer few questions a 
new student in my lab asked me. When we are doing band plot its a curve between 
k~E.? In the input file we give ka values as,
? 
?? 0.0? 0.0? 0.0? 
?? 0.0? 0.0? 0.1? 
?? 0.0? 0.0? 0.2? 
?? 0.0? 0.0? 0.3? 
?? 0.0? 0.0? 0.4? 

then what how are we getting the k values to plot the band structure. The 
values in the data file looks different from these values. 

Another question is, which unit is followed in QE? 
a.u. (hbar = e^2 = m_e = 1, energy? in Hartree)? or Rydberg unit ( hbar=1, 
e^2=2, m_e=1/2, energy in rydberg).

Sometimes the output energy is given in eV and sometimes in Rydberg. This is 
confusing that which unit is followed in QE.

please suggest on these two points. 
Regards


Padmaja Patnaik
Research Scholar
Dept of Physics
IIT Bombay
Mumbai, India
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[Pw_forum] k point value

[mohnish pandey]

Dear Padmaja,

These k-values are the k-points in high symmetry direction which you choose
to plot the band structure. Automatic grid generated for "scf" calculation
if often not suitable for band-structure plot so we choose a high symmetry
direction and discretize the reciprocal space in that direction. These are
called special k-points for band structure plot. You can write a small code
to generate a mesh with given high symmetry special k-points. And regarding
the answer to your second question the unit of the total energy is always
in Ryd. Its not a very big issue to figure out. Generally the fermi energy
and in few more cases the energy could be in eV. Hope this helps.

On Thu, Nov 17, 2011 at 11:17 PM, Padmaja Patnaik <
padmaja_patnaik at yahoo.co.uk> wrote:

> Dear all
> I am using QE since last few yeras but still could not answer few
> questions a new student in my lab asked me. When we are doing band plot its
> a curve between k~E.  In the input file we give ka values as,
>
>0.0  0.0  0.0
>0.0  0.0  0.1
>0.0  0.0  0.2
>0.0  0.0  0.3
>0.0  0.0  0.4
>
> then what how are we getting the k values to plot the band structure. The
> values in the data file looks different from these values.
>
> Another question is, which unit is followed in QE?
> a.u. (hbar = e^2 = m_e = 1, energy  in Hartree)  or Rydberg unit ( hbar=1,
> e^2=2, m_e=1/2, energy in rydberg).
>
> Sometimes the output energy is given in eV and sometimes in Rydberg. This
> is confusing that which unit is followed in QE.
>
> please suggest on these two points.
> Regards
>
> Padmaja Patnaik
> Research Scholar
> Dept of Physics
> IIT Bombay
> Mumbai, India
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 
Regards,
MOHNISH,
-
Mohnish Pandey
BTech-Mtech, IIT Kanpur
Senior Project Associate,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
-
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[Pw_forum] k point value

[Paolo Giannozzi]

On Thu, 2011-11-17 at 17:47 +, Padmaja Patnaik wrote:

> then what how are we getting the k values to plot the band structure.
> The values in the data file looks different from these values. 

if you are referring to the x axis in the plot: it is the distance 
from the first k-point, calculated along the provided k-point path.
It's what you need to get a band plot the looks like a band plot.

> Another question is, which unit is followed in QE? 
> a.u. (hbar = e^2 = m_e = 1, energy  in Hartree)  or Rydberg unit
> ( hbar=1, e^2=2, m_e=1/2, energy in rydberg).

CP uses Hartree, all other codes use Ry. Occasional usage of other 
units is typicalluy clearly stated.

P.
-- 
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy

[Pw_forum] K-point convergence help

[Ben Palmer]

Hi everyone,

I made a post some time ago asking for advice on k-point convergence, 
and I had a lot of helpful replies.  I just wanted to ask for a bit more 
help.  I've been converging for Ruthenium and a few other elements.  
They seem to converge at a smearing width of 0.05, then the 18x18x18 
breaks away from the rest at higher smearing widths.  Would this suggest 
0.05 is the sweet spot, or would it mean I'd have to continue to higher 
numbers of k-points?

Plot of force vs smearing width:

Plot of force relative to 18x18x18 k-points:

All the best,

Ben Palmer, Student @ University of Birmingham, UK
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[Pw_forum] K-point convergence help

[Abolore Musari]

dear ben
l would rather suggest u do convergence with ecut first.

its a better  way to start and remember ecutrho for ultrasoft
pseudopotential is btw 8-12 times ecutwfc
On May 25, 2013 6:04 PM, "Ben Palmer"  wrote:

> **
> Hi everyone,
>
> I made a post some time ago asking for advice on k-point convergence, and
> I had a lot of helpful replies.  I just wanted to ask for a bit more help.
> I've been converging for Ruthenium and a few other elements.  They seem to
> converge at a smearing width of 0.05, then the 18x18x18 breaks away from
> the rest at higher smearing widths.  Would this suggest 0.05 is the sweet
> spot, or would it mean I'd have to continue to higher numbers of k-points?
>
> Plot of force vs smearing width:
>
> Plot of force relative to 18x18x18 k-points:
>
> All the best,
>
> Ben Palmer, Student @ University of Birmingham, UK
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
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[Pw_forum] K-point convergence help

[Ben Palmer]

Hi Abolore,

I've converged the ecutwfc and ecutrho, then converged the k-points and 
smearing.  At 18x18x18 the calculations are starting to take a lot 
longer to run.  I was just wondering if I'd hit the sweet spot with the 
smearing at just 0.05, or whether I'd really need to continue to higher 
k-points.  Is it satisfactory to accept convergence at 0.05 for the 
smearing width as all the k-points seem to converge there?

All the best,

Ben


> dear ben
> l would rather suggest u do convergence with ecut first.
>
> its a better  way to start and remember ecutrho for ultrasoft 
> pseudopotential is btw 8-12 times ecutwfc
>
> On May 25, 2013 6:04 PM, "Ben Palmer"  > wrote:
>
> Hi everyone,
>
> I made a post some time ago asking for advice on k-point
> convergence, and I had a lot of helpful replies.  I just wanted to
> ask for a bit more help.  I've been converging for Ruthenium and a
> few other elements.  They seem to converge at a smearing width of
> 0.05, then the 18x18x18 breaks away from the rest at higher
> smearing widths.  Would this suggest 0.05 is the sweet spot, or
> would it mean I'd have to continue to higher numbers of k-points?
>
> Plot of force vs smearing width:
>
> Plot of force relative to 18x18x18 k-points:
>
> All the best,
>
> Ben Palmer, Student @ University of Birmingham, UK
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org 
> http://pwscf.org/mailman/listinfo/pw_forum
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

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[Pw_forum] K-point convergence help

[Nicola Marzari]

On 25/05/2013 19:04, Ben Palmer wrote:
> Hi everyone,
>
> I made a post some time ago asking for advice on k-point convergence,
> and I had a lot of helpful replies.  I just wanted to ask for a bit more
> help.  I've been converging for Ruthenium and a few other elements.
> They seem to converge at a smearing width of 0.05, then the 18x18x18
> breaks away from the rest at higher smearing widths.  Would this suggest
> 0.05 is the sweet spot, or would it mean I'd have to continue to higher
> numbers of k-points?
>

Dear Ben,


my gut feeling is that at large smearing widths all samplings should
give the same results - so it's a bit odd that the 18x18x18 is off
from the others. Maybe you do not have enough bands at high smearings
so that the occupation of the highest states is significantly larger 
than zero.

In any case, anything interesting is in the region between
0.005 and 0.05 - you need to decide what is the accuracy on the force
you are willing to tolerate, and choose sampling and smearing appropriately.

nicola




--
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL

[Pw_forum] K point in matdyn.x

[Mahdi Mirnezhad]

Dear All,
I want to calculate the phonon dispersion-relation with matdyn.x. What
is the unit of q-points in this code (tpiba, crystal, tpiba-b,
crystal-b)??
Best Regards,

Mahdi Mirnezhad,
Guilan University, Rasht, Iran.

[Pw_forum] K point in matdyn.x

[mohnish pandey]

Dear Mahdi,
 Your answer lies here:
http://www.democritos.it/pipermail/pw_forum/2011-May/020576.html

On Wed, May 25, 2011 at 6:37 PM, Mahdi Mirnezhad wrote:

> Dear All,
> I want to calculate the phonon dispersion-relation with matdyn.x. What
> is the unit of q-points in this code (tpiba, crystal, tpiba-b,
> crystal-b)??
> Best Regards,
>
> Mahdi Mirnezhad,
> Guilan University, Rasht, Iran.
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>



-- 
Regards,
MOHNISH,
-
Mohnish Pandey
Y6927262,5th Year dual degree student,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
-
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[Pw_forum] K point in matdyn.x

[Mahdi Mirnezhad]

Dear mohnish,
Thanks in advance for your help.

On 5/25/11, mohnish pandey  wrote:
> Dear Mahdi,
>  Your answer lies here:
> http://www.democritos.it/pipermail/pw_forum/2011-May/020576.html
>
> On Wed, May 25, 2011 at 6:37 PM, Mahdi Mirnezhad
> wrote:
>
>> Dear All,
>> I want to calculate the phonon dispersion-relation with matdyn.x. What
>> is the unit of q-points in this code (tpiba, crystal, tpiba-b,
>> crystal-b)??
>> Best Regards,
>>
>> Mahdi Mirnezhad,
>> Guilan University, Rasht, Iran.
>> ___
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>>
>
>
>
> --
> Regards,
> MOHNISH,
> -
> Mohnish Pandey
> Y6927262,5th Year dual degree student,
> Department of Chemical Engineering,
> IIT KANPUR, UP, INDIA
> -
>

[Pw_forum] K-point of silicene

[Andrey Chibisov]

Dear Colleagues.
I study silicene. My input file is:

&CONTROL
calculation ='scf',
restart_mode='from_scratch',
pseudo_dir = '/Silicene/Espresso',
outdir = '/Silicene/Espresso/temp',
/
&SYSTEM
ibrav = 4,
celldm(1) = 29.368422675588050347010890147159,
celldm(3) = 0.6781823680434460881147409128054,
nat = 32,
ntyp = 1,
ecutwfc = 36,
occupations = 'smearing',
smearing = 'gauss',
degauss = 0.02,
nosym=.true.,
nspin = 2, starting_magnetization(1) = 0.4,
nbnd =135, 
/
&ELECTRONS
conv_thr = 1.D-9,
mixing_beta = 0.3,
/
&IONS
ion_dynamics = 'bfgs',
/
&CELL
cell_dynamics = 'bfgs',
cell_dofree = 'xy',
/
ATOMIC_SPECIES
Si 28.0855 Si.UPF
ATOMIC_POSITIONS (crystal)
 Si 0.001370.001771.00011 
 Si 0.083900.168770.95815 
 Si 0.251370.001771.00011 
 Si 0.333900.168770.95815 
 Si 0.501370.001771.00011
 Si 0.583900.168770.95815 
 Si 0.751370.001771.00011
 Si 0.833900.168770.95815 
 Si 0.001370.251771.00011 
 Si 0.083900.418770.95815
 Si 0.251370.251771.00011
 Si 0.333900.418770.95815 
 Si 0.501370.251771.00011 
 Si 0.583900.418770.95815 
 Si 0.751370.251771.00011 
 Si 0.833900.418770.95815  
 Si 0.001370.501771.00011 
 Si 0.083900.668770.95815 
 Si 0.251370.501771.00011 
 Si 0.333900.668770.95815  
 Si 0.501370.501771.00011  
 Si 0.583900.668770.95815  
 Si 0.751370.501771.00011 
 Si 0.833900.668770.95815 
 Si 0.001370.751771.00011 
 Si 0.083900.918770.95815 
 Si 0.251370.751771.00011 
 Si 0.333900.918770.95815 
 Si 0.501370.751771.00011 
 Si 0.583900.918770.95815 
 Si 0.751370.751771.00011 
 Si 0.833900.918770.95815   
   
K_POINTS automatic
8 8 1 0 0 0

How I can find the K-point on the band structure?

-- 
Best regards,
Andrey Chibisov. Ph.D.
Numerical method of mathematical physics Laboratory,
Computational Center, Russian Academy of Sciences.
Khabarovsk, Russia
Web page: http://ru.linkedin.com/pub/andrey-chibisov/55/253/986/en
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[Pw_forum] k point in PHonon

[wangwy13]

Dear everyone,I have a naive question about the number of k points in PHonon calculations.I have a magnetic system (nspin=2) under calculation for the phonon DOS. The  crystal structure is bcc-like with space group number of 229 (a supercell of bcc lattice, which contains a single impurity atom) . I observe that in the output of ph.x the number of k points is doubled, compared with what was given by pw.x. I also observe that the number of k points remain the same with both codes for non-magnetic system. Does that mean magnetic systems involve some symmetry operations which must be discarded during the DFPT calculation? And does that mean the ratio of the numbers of k points must be 2:1 (N_ph : N_pw) ?(I'm using 5.4.0, if this matters)Also another naive question. How should I estimate the time cost of PHonon calculations?In the guide, it is said that "each of the 3Nat modes requires a time of the same order of magnitude of self-consistent calculation in the same system". From the source code, it appears a nscf calculation usually is necessary. So would the following formulation be correct,For each q point : t_total = t_nscf + sum_over_representations (Num_modes_each_representation * t_scf)Many thanks for your explanationYi Wang--Nanjing University of Science and Technology, China



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[Pw_forum] k point grid hybrid functionals

["Valentina Dellacà C.R.F. S.C.p.A."]

Hi,
I am having some doubts concerning nqx1,2,3 and K points grid when using 
hybrid functionals. As I understand, please let me know if I am wrong, 
there is no specific rule in how to choose the q point grid, for a given 
k point grid. The advice is to choose them to be the same, in order to 
avoid convergence issues. My question now is, since I read in hybrid 
functional README, that a shift in the q point grid is not implemented, 
can I pick a shifted k-point grid and a non shifted q point grid? Would 
it be better to pick two unshifted grids?
Thank you
best regards
Valentina
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[Pw_forum] k point grid hybrid functionals

[Lorenzo Paulatto]

On 04/15/2013 12:23 PM, "Valentina Dellac? C.R.F. S.C.p.A." wrote:
> Hi,
> I am having some doubts concerning nqx1,2,3 and K points grid when 
> using hybrid functionals. As I understand, please let me know if I am 
> wrong, there is no specific rule in how to choose the q point grid, 
> for a given k point grid. The advice is to choose them to be the same, 
> in order to avoid convergence issues. My question now is, since I read 
> in hybrid functional README, that a shift in the q point grid is not 
> implemented, can I pick a shifted k-point grid and a non shifted q 
> point grid? Would it be better to pick two unshifted grids?

Dear Valentina,
the grids are {k} and {k+q}, where the {q} grid is always 
Gamma-centered. In other words, for each k point there is a 
corresponding {k+q} grid centered around it.

There is the additional constraint that each k+q point (for every k and 
q) must be related to one of the initial k points by a G vector of the 
reciprocal lattice and eventually a symmetry operation. I think this 
condition should not cause any problem if the {k} grid is shifted, but 
I'm not 100% sure.

In the limit where the {q} grid contains only the Gamma point, than each 
k-point exchanges only with itself (not with Gamma!). In the opposite 
limit where the {q} grid has the same spacing as the {k} one (which may 
include a shift) then the {k} grid becomes equivalent to the {k+q} one, 
for every k. I.e.  the {k} grid and any {k+q} grid are just shifted and 
re-indexed w.r.t each other.

I hope this helps, it is a bit confusing but it makes sense eventually.

bests

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Universit? Paris 6
phone:+33 (0)1 44275 084 / skype: paulatz
www:  http://www-int.impmc.upmc.fr/~paulatto/
mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 5

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[Pw_forum] k point grid hybrid functionals

["Valentina Dellacà C.R.F. S.C.p.A."]

Dear Lorenzo,
thanks for your answer. I still have some doubts; when you say that

'In the limit where the {q} grid contains only the Gamma point, than
 each k-point exchanges only with itself (not with Gamma!).'

it means that the q+k grid will end up to be the k grid. But then,

'In the
 opposite limit where the {q} grid has the same spacing as the {k}
 one (which may include a shift) then the {k} grid becomes equivalent
 to the {k+q} one, for every k. I.e.  the {k} grid and any {k+q} grid
 are just shifted and re-indexed w.r.t each other. '

which is the difference with this second case? I have thought that when 
q grid and the k grid have the same spacing, the number of k+q points is 
larger than that of the k points, so they could not be equivalent.
As you see, I am a beginner and a bit confused about this topic, do you 
have any paper to recommend me?
Thank you very much,
regards

Valentina


Il 04/15/2013 01:08 PM, Lorenzo Paulatto ha scritto:
> On 04/15/2013 12:23 PM, "Valentina Dellac? C.R.F. S.C.p.A." wrote:
>> Hi,
>> I am having some doubts concerning nqx1,2,3 and K points grid when 
>> using hybrid functionals. As I understand, please let me know if I am 
>> wrong, there is no specific rule in how to choose the q point grid, 
>> for a given k point grid. The advice is to choose them to be the 
>> same, in order to avoid convergence issues. My question now is, since 
>> I read in hybrid functional README, that a shift in the q point grid 
>> is not implemented, can I pick a shifted k-point grid and a non 
>> shifted q point grid? Would it be better to pick two unshifted grids?
>
> Dear Valentina,
> the grids are {k} and {k+q}, where the {q} grid is always 
> Gamma-centered. In other words, for each k point there is a 
> corresponding {k+q} grid centered around it.
>
> There is the additional constraint that each k+q point (for every k 
> and q) must be related to one of the initial k points by a G vector of 
> the reciprocal lattice and eventually a symmetry operation. I think 
> this condition should not cause any problem if the {k} grid is 
> shifted, but I'm not 100% sure.
>
> In the limit where the {q} grid contains only the Gamma point, than 
> each k-point exchanges only with itself (not with Gamma!). In the 
> opposite limit where the {q} grid has the same spacing as the {k} one 
> (which may include a shift) then the {k} grid becomes equivalent to 
> the {k+q} one, for every k. I.e.  the {k} grid and any {k+q} grid are 
> just shifted and re-indexed w.r.t each other.
>
> I hope this helps, it is a bit confusing but it makes sense eventually.
>
> bests
>
> -- 
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS&  Universit? Paris 6
> phone:+33 (0)1 44275 084 / skype: paulatz
> www:http://www-int.impmc.upmc.fr/~paulatto/
> mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 5


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[Pw_forum] k point grid hybrid functionals

[Lorenzo Paulatto]

On 04/15/2013 02:33 PM, "Valentina Dellac? C.R.F. S.C.p.A." wrote:
> Dear Lorenzo,
> thanks for your answer. I still have some doubts; when you say that
> 'In the limit where the {q} grid contains only the Gamma point, than
>  each k-point exchanges only with itself (not with Gamma!).'
> it means that the q+k grid will end up to be the k grid. But then,

No, it does not. In fact there is not a single {k+q} grid, there is one 
for each k point. In the first case each of these grids contain a single 
point: k itself. In the second case, each of this grids contain all the 
k points, but in a different order and eventually translated by a G vector.

The second condition I stated before guarantees that k+q = Sk'+G, for 
every k and q, where k' is a point in the {k} grid, S a symmetry 
operation and G a vector of the reciprocal lattice. If you ignore 
symmetry, you can restate the condition as, it must be possible to 
express any q as q= k-k'+G, same definitions as before.

This allows to store all the {k+q} grids very efficiently, but you 
should still think of them as many different grids.
> As you see, I am a beginner and a bit confused about this topic, do 
> you have any paper to recommend me?
>
I do not have any paper where this is mechanism is explained in 
detail... maybe someone else who's reading this thread can recommend 
some reading?

bests

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Universit? Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05

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[Pw_forum] k point grid hybrid functionals

["Valentina Dellacà C.R.F. S.C.p.A."]

Dear Lorenzo,
thank you very much. Your answer is very helpful.
If someone has a paper to suggest me...thanks.
Regards,
Valentina



Il 04/15/2013 03:19 PM, Lorenzo Paulatto ha scritto:
> On 04/15/2013 02:33 PM, "Valentina Dellac? C.R.F. S.C.p.A." wrote:
>> Dear Lorenzo,
>> thanks for your answer. I still have some doubts; when you say that
>> 'In the limit where the {q} grid contains only the Gamma point, than
>>  each k-point exchanges only with itself (not with Gamma!).'
>> it means that the q+k grid will end up to be the k grid. But then,
>
> No, it does not. In fact there is not a single {k+q} grid, there is 
> one for each k point. In the first case each of these grids contain a 
> single point: k itself. In the second case, each of this grids contain 
> all the k points, but in a different order and eventually translated 
> by a G vector.
>
> The second condition I stated before guarantees that k+q = Sk'+G, for 
> every k and q, where k' is a point in the {k} grid, S a symmetry 
> operation and G a vector of the reciprocal lattice. If you ignore 
> symmetry, you can restate the condition as, it must be possible to 
> express any q as q= k-k'+G, same definitions as before.
>
> This allows to store all the {k+q} grids very efficiently, but you 
> should still think of them as many different grids.
>> As you see, I am a beginner and a bit confused about this topic, do 
>> you have any paper to recommend me?
>>
> I do not have any paper where this is mechanism is explained in 
> detail... maybe someone else who's reading this thread can recommend 
> some reading?
>
> bests
> -- 
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS&  Universit? Paris 6
> phone: +33 (0)1 44275 084 / skype: paulatz
> www:http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05


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[Pw_forum] K-point in phonon calculation

[Lo_wan_2005XW]

Dear developer and users:

Exactly follow the userguide, I am trying to calculate the phonon.

Firstly I make a self-consistent calculation with 
K_POINTS automatic
8 8 8   0  0  0

After the calculation convergent, I start the ph.x calculation. But the 
calculation is extremely slow, thus I goto
the output-file, and find a strange thing.

For some q-qoint, I find;
number of k points=  1024  Marzari-Vanderbilt smearing, width (Ry)=  0.0500

I understand that phonon may break some symmetry, but how it can go to 
1024-k-point when I use 8-8-8 mesh?

I already use "start_q=X, last_q=X, recover=.true.," to separate q-point. I 
also use parallel to speed up the calculation.
But it is still extremely slow. My system has only 12 atoms per unit cell, and 
it seems that some q-point 
(where it requires 1024 k-points) may need one month!

I don't know if there is other method to speed up the calculation?

Thanks!

Xiangang Wan



  
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[Pw_forum] K-point in phonon calculation

[程迎春]

? 2011?8?21? ??4:36?Lo_wan_2005XW ???

>  Dear developer and users:
>
> Exactly follow the userguide, I am trying to calculate the phonon.
>
> Firstly I make a self-consistent calculation with
>
> K_POINTS automatic
> 8 8 8   0  0  0
>
> After the calculation convergent, I start the ph.x calculation. But the 
> calculation is extremely slow, thus I goto
> the output-file, and find a strange thing.
>
> For some q-qoint, I find;
> number of k points=  1024  Marzari-Vanderbilt smearing, width (Ry)=  0.0500
>
> 8*8*8=512. If you set the spin polarized scf calculation, I think the
number of total k points should multiply 2 again, so there are 1024 kpoints.


>
> I understand that phonon may break some symmetry, but how it can go to 
> 1024-k-point when I use 8-8-8 mesh?
>
> I already use "start_q=X, last_q=X, recover=.true.," to separate q-point. I 
> also use parallel to speed up the calculation.
> But it is still extremely slow. My system has only 12 atoms per unit cell, 
> and it seems that some q-point
> (where it requires 1024 k-points) may need one month!
>
> I don't know if there is other method to speed up the calculation?
>
> 1,To make sure pwscf can find all symmetry operation in scf calculation.
2, To reduce the number of k points, ecut energy~
Hope it helps!

>
> Thanks!
>
> Xiangang Wan
>
>
>
>
>
> ___
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> Pw_forum at pwscf.org
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>
>


-- 
Y. C. Cheng
Department of Physics
Nanjing University
Nanjing 210093
P. R. China
Tel: 86-25-83592907
Email: yccheng.nju at gmail.com
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Re: [Pw_forum] K-point of silicene

[Ari P Seitsonen]

Dear Andrey,

  You seem to run a super-cell, ie many cells along the 2D plane: Thus 
your band structure gets folded into the small Brillouin zone, and it is 
difficult to find the bands ("Dirac point") as-is. There are references 
now in the literature for un-folding the band structure, I know of one 
tool for doing this (Jonas Björk et co, 
http://www.ifm.liu.se/theomod/compphys/band-unfolding/), or you try 
figuring out the back-folding by first thinking how the Brillouin zones of 
the (1x1) cell and your super-cell would fit and then following the bands 
in your calculation.


Greetings from Sunny Montrouge,

   apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
  Ari Paavo Seitsonen / ari.p.seitso...@iki.fi / http://www.iki.fi/~apsi/
  Ecole Normale Supérieure (ENS), Département de Chimie, Paris
  Mobile (F) : +33 789 37 24 25(CH) : +41 79 71 90 935


On Fri, 15 Jan 2016, Andrey Chibisov wrote:


Dear Colleagues.
I study silicene. My input file is:

&CONTROL
calculation ='scf',
restart_mode='from_scratch',
pseudo_dir = '/Silicene/Espresso',
outdir = '/Silicene/Espresso/temp',
/
&SYSTEM
ibrav = 4,
celldm(1) = 29.368422675588050347010890147159,
celldm(3) = 0.6781823680434460881147409128054,
nat = 32,
ntyp = 1,
ecutwfc = 36,
occupations = 'smearing',
smearing = 'gauss',
degauss = 0.02,
nosym=.true.,
nspin = 2, starting_magnetization(1) = 0.4,
nbnd =135,
/
&ELECTRONS
conv_thr = 1.D-9,
mixing_beta = 0.3,
/
&IONS
ion_dynamics = 'bfgs',
/
&CELL
cell_dynamics = 'bfgs',
cell_dofree = 'xy',
/
ATOMIC_SPECIES
Si 28.0855 Si.UPF
ATOMIC_POSITIONS (crystal)
Si 0.001370.001771.00011
Si 0.083900.168770.95815
Si 0.251370.001771.00011
Si 0.333900.168770.95815
Si 0.501370.001771.00011
Si 0.583900.168770.95815
Si 0.751370.001771.00011
Si 0.833900.168770.95815
Si 0.001370.251771.00011
Si 0.083900.418770.95815
Si 0.251370.251771.00011
Si 0.333900.418770.95815
Si 0.501370.251771.00011
Si 0.583900.418770.95815
Si 0.751370.251771.00011
Si 0.833900.418770.95815
Si 0.001370.501771.00011
Si 0.083900.668770.95815
Si 0.251370.501771.00011
Si 0.333900.668770.95815
Si 0.501370.501771.00011
Si 0.583900.668770.95815
Si 0.751370.501771.00011
Si 0.833900.668770.95815
Si 0.001370.751771.00011
Si 0.083900.918770.95815
Si 0.251370.751771.00011
Si 0.333900.918770.95815
Si 0.501370.751771.00011
Si 0.583900.918770.95815
Si 0.751370.751771.00011
Si 0.833900.918770.95815
K_POINTS automatic
8 8 1 0 0 0

How I can find the K-point on the band structure?

--
Best regards,
Andrey Chibisov. Ph.D.
Numerical method of mathematical physics Laboratory,
Computational Center, Russian Academy of Sciences.
Khabarovsk, Russia
Web page: http://ru.linkedin.com/pub/andrey-chibisov/55/253/986/en
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[Pw_forum] k point convergence of dielectric properties

[dario rocca]

Dear Users
I have an issue related to the convergence of the static dielectric  matrix
using the PH code. I have performed calculations
on bulk silicon using different k point meshes and I have obtained the
following results:

k grid  diagonal component of  number of k points in
 the dielectric tensor   the irreducible
Brillouin zone

4*4*4   23.6683500658
 6 *6*616.297485614   16
8 *8*8  14.044830694   29
10 *10*10 13.288531964 47
12*12*12  13.029602882 72
16 *16*16 12.908820645145
20 *20*20 12.894538380256

k grid+ 1 1 1 shift  diagonal component of  number of k
points in
the dielectric tensor
the irreducible Brillouin zone

4*4*4  13.840844632
  10
6*6*6
12.997009732   28
8*8*8
12.903849607   60
10*10*10   12.893711596
110
12*12*12   12.892685597
182
16*16*16   12.892482798
408
20*20*20   12.892537346
770

I was surprised of the improvement in the convergence due to the shift of
the grid. I don't think this is related to the number of k points
in the IBZ (at least not exclusively).
I have observed a similar behavior in diamond.
The ground state energy convergence also benefits from the shift, but the
improvement is not so striking.
Does someone has any hint on why the shift of the grid improves the
calculation of the dielectric properties of silicon?
Thanks a lot
Dario Rocca, dept. of chemistry, UC Davis
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[Pw_forum] k point convergence of dielectric properties

[Stefano de Gironcoli]

Dear Dario,

this is an issue related to the fact that a shifted grid in the fcc  
Bravais lattice has  lower symmetry than cubic... just think of the  
simplest 
1 1 1 1 1 1 grid that should contains one single point  L=(1/2 1/2 1/2) 
but actually represents  the 4 (rotationally but not translationally)
equivalent points (1/2 1/2 1/2), (-1/2,-1/2,1/2), 
(-1/2,1/2,-1/2),(1/2,-1/2,-1/2) . The argument can be easily extended to 
denser grids and shows that the shifted grid represents 4*N^3 points in 
the fcc BZ.
This explains why the shifted grid appears more accurate (it is actually 
denser than you think) and why the number of points it contains is 
larger than you may have thought ... In fact avoiding high symmetry 
points like the Gamma point,  contained in the unshifted grid, should 
help reducing the number of inequivalent points while instead the number 
of  shifted points for a given nominal density is larger than the number 
of unshifted ones... true, but the corresponding parent grid is actually 
4 times denser than you may have thought...and the "symmetry reductions"
factor is indeed larger for the shifted grid
for example:
shifted 4*4*4 -> 256 points in the full BZ -> 10 points in the IW 
=>  sym. red. fact. = 25.6
unshifted 4*4*4 ->  64 points in the full BZ ->   8 points in the IW =>  
sym. red. fact. = 8
 
Some time (especially if your system does not have much symmetry to 
start with) you don't really care about sampling the BZ according to a 
fully cubic symmetry but a regular grid in the 3 directions is enough.. 
in this case the use of shifted grids may results in a large amount of  
"un-needed" k-points which you may want NOT to include in the 
calculation... this annoying fact is the origin of the infamous 
nosym=.true. options that much confusion generates in most users until 
they realize what its meaning and purpose really is ... there are many 
threads on that in the archive

As to the fact that total energy are less sensitive than dielectric 
properties to k-points sampling this is a well known fact
[see for instance  S.Baroni and R. Resta, PRB 33, 7017 (1986)]

Hope this helps,

stefano
--

Stefano de Gironcoli - SISSA and DEMOCRITOS


dario rocca wrote:
> Dear Users
> I have an issue related to the convergence of the static dielectric  
> matrix using the PH code. I have performed calculations
> on bulk silicon using different k point meshes and I have obtained the 
> following results:
>
> k grid  diagonal component of  number of k points in
>  the dielectric tensor   the 
> irreducible Brillouin zone
>
> 4*4*4   23.6683500658
>  6 *6*616.297485614   16
> 8 *8*8  14.044830694   29
> 10 *10*10 13.288531964 47
> 12*12*12  13.029602882 72
> 16 *16*16 12.908820645145
> 20 *20*20 12.894538380256
>
> k grid+ 1 1 1 shift  diagonal component of  number of 
> k points in
> the dielectric 
> tensor   the irreducible Brillouin zone
>
> 4*4*4  13.840844632 
>   10
> 6*6*6 
> 12.997009732   28
> 8*8*8 
> 12.903849607   60
> 10*10*10   
> 12.893711596 110
> 12*12*12   
> 12.892685597 182
> 16*16*16   
> 12.892482798 408
> 20*20*20   
> 12.892537346 770
>  
> I was surprised of the improvement in the convergence due to the shift 
> of the grid. I don't think this is related to the number of k points
> in the IBZ (at least not exclusively).
> I have observed a similar behavior in diamond.
> The ground state energy convergence also benefits from the shift, but 
> the improvement is not so striking.
> Does someone has any hint on why the shift of the grid improves the 
> calculation of the dielectric properties of silicon?
> Thanks a lot
> Dario Rocca, dept. of chemistry, UC Davis
>
> 
>
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[Pw_forum] k point convergence of dielectric properties

[Prasenjit Ghosh]

Dear Dario,

For calculation of dielectric properties you need to do integrations over
the BZ. For high symmetry lattices, a shifted k-point mesh (specially a k-pt
mesh without Gamma pt.) without the high symmetry points should be used. In
that way you have a better sampling of your BZ and hence a improvement in
the results. I also found similar improvements of convergence when I tested
for convergence of adsorption energy wrt k-point mesh.

Prasenjit.

2008/10/10 dario rocca 

>
> Dear Users
> I have an issue related to the convergence of the static dielectric  matrix
> using the PH code. I have performed calculations
> on bulk silicon using different k point meshes and I have obtained the
> following results:
>
> k grid  diagonal component of  number of k points in
>  the dielectric tensor   the irreducible
> Brillouin zone
>
> 4*4*4   23.6683500658
>  6 *6*616.297485614   16
> 8 *8*8  14.044830694   29
> 10 *10*10 13.288531964 47
> 12*12*12  13.029602882 72
> 16 *16*16 12.908820645145
> 20 *20*20 12.894538380256
>
> k grid+ 1 1 1 shift  diagonal component of  number of k
> points in
> the dielectric tensor
> the irreducible Brillouin zone
>
> 4*4*4  13.840844632
>   10
> 6*6*6
> 12.997009732   28
> 8*8*8
> 12.903849607   60
> 10*10*10   12.893711596
> 110
> 12*12*12   12.892685597
> 182
> 16*16*16   12.892482798
> 408
> 20*20*20   12.892537346
> 770
>
> I was surprised of the improvement in the convergence due to the shift of
> the grid. I don't think this is related to the number of k points
> in the IBZ (at least not exclusively).
> I have observed a similar behavior in diamond.
> The ground state energy convergence also benefits from the shift, but the
> improvement is not so striking.
> Does someone has any hint on why the shift of the grid improves the
> calculation of the dielectric properties of silicon?
> Thanks a lot
> Dario Rocca, dept. of chemistry, UC Davis
>
>
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>


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POST-DOC,
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[Pw_forum] k point convergence of dielectric properties

[Nicola Marzari]

Dario,


great detective work - and more remarkable than I would have
guessed (although I've been a fan for years of the shifted grids).

What Stefano said so clearly is related to the original idea of Alfonso
Baldereschi (PRB 7, 5121 (1973)) and generalized by Chadi and Cohen (PRB
8, 5747 (1973) - interestingly written in Paris VI Jussieu) - i.e. how 
to choose a single, special k-point (Baldereschi) or meshes of them
(Chadi and Cohen) in order to get the most accurate average. Basically,
a function f(k) that has the symmetry f the crystal, fourier expanded in
plane waves exp (i k.R) (R lattice vectors), can be rewritten as a
linear combination of symmetrized stars of plane waves (you bunch
together all the plane waves that have the same modulus for R, paying
some attention to degenerate shells that have different symmetry). By
choosing k's such that the largest number of those symmetrized stars
(sum exp (i k.R), sum over the R of a star) are zero, you have a recipe
that gives accurate integrals

Stefano de Gironcoli wrote:
> ... this annoying fact is the origin of the infamous 
> nosym=.true. options that much confusion generates in most users until 
> they realize what its meaning and purpose really is ... there are many 
> threads on that in the archive

A god-blessing ! Try it - instead of using a 2x2x2 shifted mesh (4 
k-points, if no symmetry is present beside time reversal) use only 1
point, and stop the code from symmetrizing it using nosym=true.

The results will be very close to the full mesh, at 1/4 of the cost.

nicola

-
Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

[Pw_forum] k-point grids...and all that

[Paul M. Grant]

Not to be tedious, but let me raise this question again.  First of all,
k-point.f90 is a routine I've been writing for my own education, and in the
bleariness of a late evening posting, I subliminally substituted it for
kpoints.f.  I did have a quick look at the latter code beforehand, but when
I saw the phrase "special points," I took it to refer to the
Bouckaert-Smolukowski-Wigner notation for high symmetry BZ "special points"
I learned in my younger years (this is the sort of stuff you can find on the
Bilbao website these days).  I do see now the usage of the term in kpoints.f
indeed means the calculation of an MP mesh.  Thanks, Paolo.

What I was most concerned about was the generation of k-point meshes or nets
for use as input to pw.x (nscf) for subsequent post-processing calculations,
such as the computation of Fermi surfaces or optical properties. For
example, the routine kvecs_FS.x appears to fill the reciprocal lattice of
its input structure with uniformly spaced, equally weighted, point
coordinates, whereas the method used to calculate the mesh used for the
aluminum example of epsilon.x is unclear (at least to me).  There is a
warning in the documentation for epsilon.x that "reduction of the k-points
grid into the irreducible BZ" is not supported.  I also note that the
conventional unit cell (ibrav = 1), not the Bravais or primitive fcc (ibrav
= 2) coordinates are used in the example.  Does this mean one can compute
the mesh for epsilon.x using kvecs_FS.x and the "conventional" reciprocal
cell coordinates?

Finally, on the point of mesh visualization.  I use XCrySDen a lot,
especially for BZ and charge-potential visualizations.  But I don't know how
to configure or generate a .xsf file for a 3D mesh of discrete points.

Paul M. Grant, PhD
Principal, W2AGZ Technologies
Visiting Scholar, Applied Physics, Stanford (2005-2008)
EPRI Science Fellow (Retired)
IBM Research Staff Member Emeritus
w2agz at pacbell.net
http://www.w2agz.com
?
?

-Original Message-
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-boun...@pwscf.org] On
Behalf Of Paolo Giannozzi
Sent: Monday, September 15, 2008 1:33 AM
To: PWSCF Forum
Subject: Re: [Pw_forum] k-point grids...and all that

On Sep 15, 2008, at 5:30 , Paul M. Grant wrote:
> The ability to compute weighted 1st BZ grids according to the  
> Monkhorst-Pack scheme is included somewhere within espresso-4.0,  
> but exactly where is unclear (k-points.f90?  No).
>
of course no, since it is non-existent:
$ ls -l */k-points.f90
ls: */k-points.f90: No such file or directory
There is however an auxiliary code, pwtools/kpoints.f, that produces  
Monkhorst-Pack
grids with weights (executable: kpoints.x).

Inside q-e, there are several routines for the generation of  
automatic k-point grids.
See PW/setup.f90, under
   !
   ! ... Automatic generation of k-points (if required)
   !
Routines kpoint_grid_efield and kp_strings are specific for  
macroscopic field
and Berry phase calculations; kpoint_grid and setupkpoint (undocumented)
take care of the typical scf case. The difference between the two is  
just
aesthetic.
> Finally, is there a visualization tool to display the k-point  
> distribution within the  1st BZ?  XcrysDen?
>
for sure: see http://www.xcrysden.org/img/xcrysden-in-action.png,  
first picture

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222



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[Pw_forum] k-point grids...and all that

[Paolo Giannozzi]

On Oct 13, 2008, at 6:37 , Paul M. Grant wrote:

> [...] the method used to calculate the mesh used for the
> aluminum example of epsilon.x is unclear (at least to me).

which aluminum example of epsilon.x you are referring to?

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

[Pw_forum] k-point grids...and all that

[Deyu Lu]

>Finally, on the point of mesh visualization.  I use XCrySDen a lot,
>especially for BZ and charge-potential visualizations.  But I don't know how
>to configure or generate a .xsf file for a 3D mesh of discrete points.

W.r.t. visualization of k-points, if the coordinates of k-points and the 
boundary
of the BZ are known, they can be visualized in VMD with the .xyz file format.
Below is an example of the 10 fcc special k-points (blue spheres) in the 
irreducible wedge (white spheres).

http://picasaweb.google.com/deyu.lu/Misc#5257056499972518002

Best
Deyu Lu


***
Deyu Lu (Ph.D)
190 Chemistry Building
University of California, Davis 
One Shields Avenue
Davis, CA 95616
Office phone: (530) 754-9663
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***