Re: [Pw_forum] Application of electric field to quantum dot

[Parham Shenavar]

Dear Mortars

Thank you for guidelines. I concluded that if I replace the line

K_POINTS gamma

With line similar to the following

K_POINTS
1 1 1 1 1 1

I will be able to do the berry phase calculations with pw.x program. Is it
true?

Cordially yours

Parham Shenavar
Electronic Engineering
Shiraz university,

On Jul 23, 2016 7:27 PM, "Mostafa Youssef"  wrote:

> Dear Parham,
>
> I never studied quantum dots , so I cannot give a particular
> recommendation. But for the electric field in Berry phase formalism I can
> say that Gamma point only is not implemented in pw.x but it the default and
> only option in cp.x.  In pw.x you can use one  kpoint but it has to be
> shifted (not gamma).
>
> >From my  experience nberrycyc beyond 2 does not change any of the
> calculated properties I have tested. Even the default 1 is great.
>
> It is up to you to decide how much field you need to apply. But there is a
> "computational" maximum  that can be estimated by   Egap/(L x k)
>
> Egap: band gap
> L: supercell length
> K: kpoints along the length L
>
>
> Regards,
> Mostafa
> MIT
>
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Re: [Pw_forum] Turbo TDDFT for a quantum dot

[SungHwan Choi]

Dear Dario,
Thank you for a kind reply. You mean that if it is converged without
smearing option, then there is no problem on doing turboTDDF calculation.
Am I correct?
Sincerely,
Sunghwan Choi



Sunghwan Choi
Ph.D candidate
Computational Quantum Molecular Science Lab
Department of Chemistry, KAIST, Republic of Korea

2016-07-23 16:43 GMT+09:00 dario rocca :

> Dear Sunghwan,
> I have not used the code on systems with the characteristics you describe.
> This is my guess: As far as the ground state of your quantum dot converges
> without a smearing the turboTDDFT code can be used and will be stable.
> While the independent electron polarizability of a 0 gap system diverges
> for \omega-->0, the Hartree part in the TDDFT kernel will increase the
> value of the gap and/or will "push" the oscillator strength to higher
> energies.
> Best,
> Dario
>
>
> On Fri, Jul 22, 2016 at 6:37 PM, SungHwan Choi 
> wrote:
>
>> Dear all,
>> I am checking whether turboTDDFT program is suitable for my project. My
>> project is to calculate absorption spectrum of metallic quantum dot. I have
>> two questions.
>>
>> 1) From other post, I read the fact that turboTDDFT cannot calculate a
>> metallic system. Here, how do we define metallic system? just system that
>> have no band gap? then for small metallic quantum dot can be a non-metallic
>> system since it has small band gap (0.1~0.5eV). case that fractional
>> occupation does not happen? then, we can control the occupation parameter
>> not to make fractional occupation.
>>
>> 2) A metallic quantum dot has a size-dependency for band gap. Thus, if
>> size become larger, then band gap become narrow. When turboTDDFT failed to
>> predict an absorption spectrum? and do you know a numerical trend of
>> artifact, which come from low band gap?
>>
>> By the way, does this limit come from algorithm or implementation of
>> turboTDDFT? As far as I understood there is no limit of algorithm itself. I
>> think there is some practical issues on there. Would you tell me where some
>> troubles come up?
>>
>> Sincerely
>> Sunghwan Choi
>>
>>
>> 
>> Sunghwan Choi
>> Ph.D candidate
>> Computational Quantum Molecular Science Lab
>> Department of Chemistry, KAIST, Republic of Korea
>>
>>
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[Pw_forum] problem hybrid pseudopotential calculations

[Muhammad Adnan Saqlain]

Dear users
I have been to vc-relax my system with hybrid pseudopotentials. However, I
always end up with this error message.


 %%
 Error in routine electrons (1):
 dexx is negative!  Check that exxdiv_treatment is appropriate for the
system.
 %%


Although, in previous emails, I was suggested to turn off
x_gamma_interpolation. However, this is not solving my problem. The first
BFGS cycle runs smooth. However, in the second cycle I get this error
message. The pw.input and pw.out file attached.
I shall be grateful if anyone can help me to solve this issue.

-- 
Best Regards
Muhammad Adnan Saqlain


pw.out
Description: Binary data


pw.inp
Description: Binary data
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[Pw_forum] problem in hybrid pseudopotential calculations

[Muhammad Adnan Saqlain]

Dear users
I have been to vc-relax my system with hybrid pseudopotentials. However, I
always end up with this error message.


 %%
 Error in routine electrons (1):
 dexx is negative!  Check that exxdiv_treatment is appropriate for the
system.
 %%


Although, in previous emails, I was suggested to turn off
x_gamma_interpolation. However, this is not solving my problem. The first
BFGS cycle runs smooth. However, in the second cycle I get this error
message. The pw.input and pw.out file attached.
I shall be grateful if anyone can help me to solve this issue.


-- 
Best Regards
Muhammad Adnan Saqlain
PhD. UFJF. Brazil
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[Pw_forum] ATOM-RESOLVED

[Suza W]

 Hi,

 Is it possible to obtain atom-resolved vibrational density of states using
QE?

Thanks,
>
Suza

>
>
> PhD, Research Fellow,
>
> Department of Physics and Materials Science,
>
> City University of Hong Kong
>
> Tel: +852 3442 4000
>
> Fax:+852 3442 0538
> 
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[Pw_forum] Graphene kpoint shift for scf and nscf calculation?

[Rolly Ng]

Dear QE users,

 

I am working on metal doped graphene and I would like to know the correct
way of setting up the K-point grid for scf and nscf calculation.

 

For scf, I have used:

K_POINTS {automatic}

  6 6 1 0 0 0

 

But for nscf, I am not sure, will shifting x y directions gives better
result?

K_POINTS {automatic}

  6 6 1 1 1 0

 

I have read P. E. Bloechl et al, PRB49, 16223 (1994) but I cannot get a
clear picture.

 

Thanks,

Rolly Ng

 

PhD, Research Fellow,

Department of Physics and Materials Science,

City University of Hong Kong

Tel: +852 3442 4000

Fax:+852 3442 0538

 

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Re: [Pw_forum] Application of electric field to quantum dot

[Mostafa Youssef]

Dear Parham,

I never studied quantum dots , so I cannot give a particular recommendation. 
But for the electric field in Berry phase formalism I can say that Gamma point 
only is not implemented in pw.x but it the default and only option in cp.x.  In 
pw.x you can use one  kpoint but it has to be shifted (not gamma).

>From my  experience nberrycyc beyond 2 does not change any of the calculated 
>properties I have tested. Even the default 1 is great.

It is up to you to decide how much field you need to apply. But there is a 
"computational" maximum  that can be estimated by   Egap/(L x k)

Egap: band gap
L: supercell length
K: kpoints along the length L


Regards,
Mostafa
MIT
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Re: [Pw_forum] problem hybrid pseudopotential calculations

[Muhammad Adnan Saqlain]

Dear Stefano
Thanks for your mail.
But what does this error mean? when I try to run the calculation, it ejects
this error? How can I get rid of it
Error in routine setup (1):
 Variable cell and EXX not tested!
The input file is as under

 &CONTROL
   title = 'CsPbI' ,
 calculation = 'vc-relax' ,
restart_mode = 'from_scratch' ,
  outdir = '/work/saqlain' ,
  wfcdir = '/work/saqlain' ,
  pseudo_dir = '/home/ibm/proj/proj527/saqlain/psp' ,
  prefix = 'PBE0' ,
 /
 &SYSTEM
   ibrav = 0,
   celldm(1) = 1.8897265,
 nat = 5,
ntyp = 3,
 ecutwfc = 40 ,
   input_dft = 'PBE0' ,
 occupations = 'smearing' ,
 degauss = 0.001 ,
smearing = 'marzari-vanderbilt' ,
ecutfock = 40 ,
exxdiv_treatment = 'none' ,
nqx1 = 2 ,
nqx2 = 2 ,
nqx3 = 2 ,
 /
 &ELECTRONS
 /
 &IONS
 /
&CELL
 /
CELL_PARAMETERS cubic
 6.3824349870.00.0
 0.06.3824349870.0
 0.00.06.382434987
ATOMIC_SPECIES
   Cs  132.9  Cs.pbe-sp-hgh.UPF
I  126.9  I.pbe-hgh.UPF
   Pb  207.2  Pb.pbe-hgh.UPF
ATOMIC_POSITIONS crystal
   Cs  0.50.50.5
I  0.50.00.0
I  0.00.50.0
I  0.00.00.5
   Pb  0.00.00.0
K_POINTS automatic
  2 2 2   1 1 1


On Sat, Jul 23, 2016 at 6:48 PM, stefano de gironcoli 
wrote:

> On 23/07/2016 14:23, Muhammad Adnan Saqlain wrote:
>
> Dear Stefano
> thanks for your response.
> Can you please guide me (1) Why vc-relax is not allowed in  Q-E 5.4.0?
>
> it is.
>
> (2) How would the band gap be effected if I relax the cell without hybrid
> scheme and then calculate band gap with hybrid one?
>
> it would be the band gap of a different structure.
> it would depend on how different the structure would be with a different
> functional.
>
> stefano
>
>
> On Sat, Jul 23, 2016 at 1:07 PM, stefano de gironcoli 
> wrote:
>
>> dear Muhammad Adnan Saqlain,
>>
>>gamma extrapolation is a way to deal with the ill defined value of the
>> exchange integral between wfcs at k and k+q in the limit of q->0.
>>if you use a truncated coulomb interaction that limit is not ill
>> defined.
>>no need to use the gamma_extrapolation option
>>best,
>> stefano
>>
>> On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:
>>
>> Dear Prof Clavijo
>> I am extremely sorry for my misleading title of the calculation.
>> Actually, It was a cubic structure consisting of Cs, Pb and I. I
>> deliberately did not put the atoms in the calculation. more over I do not
>> know why the algorithm for cell movement was not copied it was however
>> present in the input file.
>>
>> 1. If I try these two options, the
>>
>> vcut_spherical : appropriate for cubic and quasi-cubic supercells
>> vcut_ws : appropriate for strongly anisotropic supercells, see also
>>   ecutvcut.
>>
>> the program says like this
>>
>>
>> %%
>>  Error in routine  system_checkin (1):
>>   x_gamma_extrapolation cannot be used with vcut
>>
>>  
>> %%
>>
>> I have no idea how to fix it. Can you suggest one??
>>
>> 2. I have now used Q-E 5.4.0, but this version does not allow vc-relax
>> option with hybrid one. why is it so? How would the band gap be effected if
>> I relax the cell without hybrid scheme and then calculate band gap with
>> hybrid one?
>>
>> 3. About the ecutoff, I deliberately used small one as these are just
>> calculations not the real one.
>> 4. I have cubic system, may I try q-grid like 1*2*3 or it has to be
>> symmetric one?
>>  5. Can you suggest more about hybrid calculations?
>>
>>
>> On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos <
>> jiclavi...@unal.edu.co> wrote:
>>
>>> Dear, Muhammad Adnan Saqlain, remember the user documentation for
>>> *exxdiv_treatment*:
>>>
>>> Specific for EXX. It selects the kind of approach to be used
>>> for treating the Coulomb potential divergencies at small q vectors.
>>>
>>> gygi-baldereschi : appropriate for cubic and *quasi-cubic supercells*
>>> vcut_spherical : appropriate for cubic and quasi-cubic supercells
>>> vcut_ws : appropriate for strongly anisotropic supercells, see also
>>>   ecutvcut.
>>> none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)
>>>
>>> *Besides that, *I have some observations and suggestions for you based
>>> in the input file you send, so you can real

Re: [Pw_forum] problem hybrid pseudopotential calculations

[stefano de gironcoli]

On 23/07/2016 14:23, Muhammad Adnan Saqlain wrote:

Dear Stefano
thanks for your response.
Can you please guide me (1) Why vc-relax is not allowed in  Q-E 5.4.0?

it is.
(2) How would the band gap be effected if I relax the cell without 
hybrid scheme and then calculate band gap with hybrid one?



it would be the band gap of a different structure.
it would depend on how different the structure would be with a different 
functional.


stefano


On Sat, Jul 23, 2016 at 1:07 PM, stefano de gironcoli 
mailto:degir...@sissa.it>> wrote:


dear Muhammad Adnan Saqlain,

   gamma extrapolation is a way to deal with the ill defined value
of the exchange integral between wfcs at k and k+q in the limit of
q->0.
   if you use a truncated coulomb interaction that limit is not
ill defined.
   no need to use the gamma_extrapolation option
   best,
stefano

On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:

Dear Prof Clavijo
I am extremely sorry for my misleading title of the calculation.
Actually, It was a cubic structure consisting of Cs, Pb and I. I
deliberately did not put the atoms in the calculation. more over
I do not know why the algorithm for cell movement was not copied
it was however present in the input file.

1. If I try these two options, the

vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
   ecutvcut.

the program says like this


%%
 Error in routine  system_checkin (1):
  x_gamma_extrapolation cannot be used with vcut
 
%%

I have no idea how to fix it. Can you suggest one??

2. I have now used Q-E 5.4.0, but this version does not allow
vc-relax option with hybrid one. why is it so? How would the band
gap be effected if I relax the cell without hybrid scheme and
then calculate band gap with hybrid one?

3. About the ecutoff, I deliberately used small one as these are
just calculations not the real one.
4. I have cubic system, may I try q-grid like 1*2*3 or it has to
be symmetric one?
 5. Can you suggest more about hybrid calculations?


On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos
mailto:jiclavi...@unal.edu.co>> wrote:

Dear, Muhammad Adnan Saqlain, remember the user documentation
for *exxdiv_treatment*:

Specific for EXX. It selects the kind of approach to be used
for treating the Coulomb potential divergencies at small q vectors.

gygi-baldereschi : appropriate for cubic and*quasi-cubic supercells*
vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
   ecutvcut.
none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)

*Besides that, *I**have some observations and suggestions for
you based in the input file you send, so you can realize why
does QE is failing when trying to simulate your system:

1 - Check if you really need to apply smearing, since this
technique is intended to be useful for metallic systems, and
Anatase is cleary not a metallic system, in fact, is more a
Wide-gap or Insulator -type system.

2 - You do want to perform a vc-relax calculation, but
nothing are specified in the cards &IONS and &CELL. There is
not cell relaxing algorithm specified (BFGS? MD?)

3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no
cell to relax.

4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble
opinion, a very poor cutoff for a serious calculation. Do
a ecutwfc convergence test before attempt your system.

5 - Please take in account that a hybrid calculation is VERY
expensive in terms of computational demand, so if you set up
a vc-relax calculation using hybrid PPS you must test if
*nqx1 = 1, 2 or 3 really makes a difference.*
*
*
*6 - For some systems, input_dft=HSE is faster than
**input_dft = "PBE0". Check if that could be your case.*
*
*
By the way, are you sure Anatase has a cubic crystal
structure? Does XCrysden show the correct structure for your
input?

*Best regards, *
*
*

Josué Clavijo, PhD.
Assistant Professor
Universidad Nacional de Colombia
Departamento de Química

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-- 
Best Regar

Re: [Pw_forum] problem hybrid pseudopotential calculations

[Muhammad Adnan Saqlain]

Dear Stefano
thanks for your response.
Can you please guide me (1) Why vc-relax is not allowed in  Q-E 5.4.0?
(2) How would the band gap be effected if I relax the cell without hybrid
scheme and then calculate band gap with hybrid one?


On Sat, Jul 23, 2016 at 1:07 PM, stefano de gironcoli 
wrote:

> dear Muhammad Adnan Saqlain,
>
>gamma extrapolation is a way to deal with the ill defined value of the
> exchange integral between wfcs at k and k+q in the limit of q->0.
>if you use a truncated coulomb interaction that limit is not ill
> defined.
>no need to use the gamma_extrapolation option
>best,
> stefano
>
> On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:
>
> Dear Prof Clavijo
> I am extremely sorry for my misleading title of the calculation. Actually,
> It was a cubic structure consisting of Cs, Pb and I. I deliberately did not
> put the atoms in the calculation. more over I do not know why the algorithm
> for cell movement was not copied it was however present in the input file.
>
> 1. If I try these two options, the
>
> vcut_spherical : appropriate for cubic and quasi-cubic supercells
> vcut_ws : appropriate for strongly anisotropic supercells, see also
>   ecutvcut.
>
> the program says like this
>
>
> %%
>  Error in routine  system_checkin (1):
>   x_gamma_extrapolation cannot be used with vcut
>
>  
> %%
>
> I have no idea how to fix it. Can you suggest one??
>
> 2. I have now used Q-E 5.4.0, but this version does not allow vc-relax
> option with hybrid one. why is it so? How would the band gap be effected if
> I relax the cell without hybrid scheme and then calculate band gap with
> hybrid one?
>
> 3. About the ecutoff, I deliberately used small one as these are just
> calculations not the real one.
> 4. I have cubic system, may I try q-grid like 1*2*3 or it has to be
> symmetric one?
>  5. Can you suggest more about hybrid calculations?
>
>
> On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos <
> jiclavi...@unal.edu.co> wrote:
>
>> Dear, Muhammad Adnan Saqlain, remember the user documentation for
>> *exxdiv_treatment*:
>>
>> Specific for EXX. It selects the kind of approach to be used
>> for treating the Coulomb potential divergencies at small q vectors.
>>
>> gygi-baldereschi : appropriate for cubic and *quasi-cubic supercells*
>> vcut_spherical : appropriate for cubic and quasi-cubic supercells
>> vcut_ws : appropriate for strongly anisotropic supercells, see also
>>   ecutvcut.
>> none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)
>>
>> *Besides that, *I have some observations and suggestions for you based
>> in the input file you send, so you can realize why does QE is failing when
>> trying to simulate your system:
>>
>> 1 - Check if you really need to apply smearing, since this technique is
>> intended to be useful for metallic systems, and Anatase is cleary not a
>> metallic system, in fact, is more a Wide-gap or Insulator -type system.
>>
>> 2 - You do want to perform a vc-relax calculation, but nothing are
>> specified in the cards &IONS and &CELL. There is not cell relaxing
>> algorithm specified (BFGS? MD?)
>>
>> 3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to relax.
>>
>> 4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble opinion, a
>> very poor cutoff for a serious calculation. Do a ecutwfc convergence test
>> before attempt your system.
>>
>> 5 - Please take in account that a hybrid calculation is VERY expensive in
>> terms of computational demand, so if you set up a vc-relax calculation
>> using hybrid PPS you must test if *nqx1 = 1, 2 or 3 really makes a
>> difference.*
>>
>> *6 - For some systems, input_dft=HSE is faster than **input_dft =
>> "PBE0". Check if that could be your case.*
>>
>> By the way, are you sure Anatase has a cubic crystal structure? Does
>> XCrysden show the correct structure for your input?
>>
>> *Best regards, *
>>
>>
>> Josué Clavijo, PhD.
>> Assistant Professor
>> Universidad Nacional de Colombia
>> Departamento de Química
>>
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>>
>
>
>
> --
> Best Regards
> Muhammad Adnan Saqlain
>
>
>
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-- 
Best Regards
Muhammad Adnan Saqlain
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[Pw_forum] Fermi surface plotting

[Suman Sardar]

Dear all,
I want to plot fermi surface by using quantum espresso.Can any
one tell me the successive step for this plotting.



Regards

Suman Sardar
IISERB
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[Pw_forum] Application of electric field to quantum dot

[Parham Shenavar]

Dear all

I did charge analysis on a quantum dot using gamma point only. I want study
of charge analysis under influence of a constant electric field using
lelfield=.true. option.

1. Is it possible? I found a lot of examples that deal with k-points while
I am only using gamma point.

2. If I want field in X direction, I should set gdir=1 but how can I have a
good estimate for efield value?

3. Is it mandatory to set nberrycyc other than its default value?

Sorry if my questions are very elementary.

Parham Shenavar
Electronic Engineering Department
School of Electrical and Computer Engineering
Shiraz university
Shiraz, Iran
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Re: [Pw_forum] problem hybrid pseudopotential calculations

[stefano de gironcoli]

dear Muhammad Adnan Saqlain,

   gamma extrapolation is a way to deal with the ill defined value of 
the exchange integral between wfcs at k and k+q in the limit of q->0.
   if you use a truncated coulomb interaction that limit is not ill 
defined.

   no need to use the gamma_extrapolation option
   best,
stefano

On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:

Dear Prof Clavijo
I am extremely sorry for my misleading title of the calculation. 
Actually, It was a cubic structure consisting of Cs, Pb and I. I 
deliberately did not put the atoms in the calculation. more over I do 
not know why the algorithm for cell movement was not copied it was 
however present in the input file.


1. If I try these two options, the

vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
   ecutvcut.

the program says like this

%%
 Error in routine  system_checkin (1):
  x_gamma_extrapolation cannot be used with vcut
 %%

I have no idea how to fix it. Can you suggest one??

2. I have now used Q-E 5.4.0, but this version does not allow vc-relax 
option with hybrid one. why is it so? How would the band gap be 
effected if I relax the cell without hybrid scheme and then calculate 
band gap with hybrid one?


3. About the ecutoff, I deliberately used small one as these are just 
calculations not the real one.
4. I have cubic system, may I try q-grid like 1*2*3 or it has to be 
symmetric one?

 5. Can you suggest more about hybrid calculations?


On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos 
mailto:jiclavi...@unal.edu.co>> wrote:


Dear, Muhammad Adnan Saqlain, remember the user documentation for
*exxdiv_treatment*:

Specific for EXX. It selects the kind of approach to be used
for treating the Coulomb potential divergencies at small q vectors.

gygi-baldereschi : appropriate for cubic and*quasi-cubic supercells*
vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
   ecutvcut.
none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)

*Besides that, *I**have some observations and suggestions for you
based in the input file you send, so you can realize why does QE
is failing when trying to simulate your system:

1 - Check if you really need to apply smearing, since this
technique is intended to be useful for metallic systems, and
Anatase is cleary not a metallic system, in fact, is more a
Wide-gap or Insulator -type system.

2 - You do want to perform a vc-relax calculation, but nothing are
specified in the cards &IONS and &CELL. There is not cell relaxing
algorithm specified (BFGS? MD?)

3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to
relax.

4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble
opinion, a very poor cutoff for a serious calculation. Do
a ecutwfc convergence test before attempt your system.

5 - Please take in account that a hybrid calculation is VERY
expensive in terms of computational demand, so if you set up a
vc-relax calculation using hybrid PPS you must test if *nqx1 = 1,
2 or 3 really makes a difference.*
*
*
*6 - For some systems, input_dft=HSE is faster than **input_dft =
"PBE0". Check if that could be your case.*
*
*
By the way, are you sure Anatase has a cubic crystal structure?
Does XCrysden show the correct structure for your input?

*Best regards, *
*
*

Josué Clavijo, PhD.
Assistant Professor
Universidad Nacional de Colombia
Departamento de Química

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Muhammad Adnan Saqlain



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Re: [Pw_forum] problem hybrid pseudopotential calculations

[Muhammad Adnan Saqlain]

Dear Prof Clavijo
I am extremely sorry for my misleading title of the calculation. Actually,
It was a cubic structure consisting of Cs, Pb and I. I deliberately did not
put the atoms in the calculation. more over I do not know why the algorithm
for cell movement was not copied it was however present in the input file.

1. If I try these two options, the

vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
  ecutvcut.

the program says like this

%%
 Error in routine  system_checkin (1):
  x_gamma_extrapolation cannot be used with vcut
 %%

I have no idea how to fix it. Can you suggest one??

2. I have now used Q-E 5.4.0, but this version does not allow vc-relax
option with hybrid one. why is it so? How would the band gap be effected if
I relax the cell without hybrid scheme and then calculate band gap with
hybrid one?

3. About the ecutoff, I deliberately used small one as these are just
calculations not the real one.
4. I have cubic system, may I try q-grid like 1*2*3 or it has to be
symmetric one?
 5. Can you suggest more about hybrid calculations?


On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos <
jiclavi...@unal.edu.co> wrote:

> Dear, Muhammad Adnan Saqlain, remember the user documentation for
> *exxdiv_treatment*:
>
> Specific for EXX. It selects the kind of approach to be used
> for treating the Coulomb potential divergencies at small q vectors.
>
> gygi-baldereschi : appropriate for cubic and *quasi-cubic supercells*
> vcut_spherical : appropriate for cubic and quasi-cubic supercells
> vcut_ws : appropriate for strongly anisotropic supercells, see also
>   ecutvcut.
> none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)
>
> *Besides that, *I have some observations and suggestions for you based in
> the input file you send, so you can realize why does QE is failing when
> trying to simulate your system:
>
> 1 - Check if you really need to apply smearing, since this technique is
> intended to be useful for metallic systems, and Anatase is cleary not a
> metallic system, in fact, is more a Wide-gap or Insulator -type system.
>
> 2 - You do want to perform a vc-relax calculation, but nothing are
> specified in the cards &IONS and &CELL. There is not cell relaxing
> algorithm specified (BFGS? MD?)
>
> 3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to relax.
>
> 4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble opinion, a
> very poor cutoff for a serious calculation. Do a ecutwfc convergence test
> before attempt your system.
>
> 5 - Please take in account that a hybrid calculation is VERY expensive in
> terms of computational demand, so if you set up a vc-relax calculation
> using hybrid PPS you must test if *nqx1 = 1, 2 or 3 really makes a
> difference.*
>
> *6 - For some systems, input_dft=HSE is faster than **input_dft = "PBE0".
> Check if that could be your case.*
>
> By the way, are you sure Anatase has a cubic crystal structure? Does
> XCrysden show the correct structure for your input?
>
> *Best regards, *
>
>
> Josué Clavijo, PhD.
> Assistant Professor
> Universidad Nacional de Colombia
> Departamento de Química
>
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Muhammad Adnan Saqlain
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Re: [Pw_forum] Turbo TDDFT for a quantum dot

[dario rocca]

Dear Sunghwan,
I have not used the code on systems with the characteristics you describe.
This is my guess: As far as the ground state of your quantum dot converges
without a smearing the turboTDDFT code can be used and will be stable.
While the independent electron polarizability of a 0 gap system diverges
for \omega-->0, the Hartree part in the TDDFT kernel will increase the
value of the gap and/or will "push" the oscillator strength to higher
energies.
Best,
Dario


On Fri, Jul 22, 2016 at 6:37 PM, SungHwan Choi 
wrote:

> Dear all,
> I am checking whether turboTDDFT program is suitable for my project. My
> project is to calculate absorption spectrum of metallic quantum dot. I have
> two questions.
>
> 1) From other post, I read the fact that turboTDDFT cannot calculate a
> metallic system. Here, how do we define metallic system? just system that
> have no band gap? then for small metallic quantum dot can be a non-metallic
> system since it has small band gap (0.1~0.5eV). case that fractional
> occupation does not happen? then, we can control the occupation parameter
> not to make fractional occupation.
>
> 2) A metallic quantum dot has a size-dependency for band gap. Thus, if
> size become larger, then band gap become narrow. When turboTDDFT failed to
> predict an absorption spectrum? and do you know a numerical trend of
> artifact, which come from low band gap?
>
> By the way, does this limit come from algorithm or implementation of
> turboTDDFT? As far as I understood there is no limit of algorithm itself. I
> think there is some practical issues on there. Would you tell me where some
> troubles come up?
>
> Sincerely
> Sunghwan Choi
>
>
> 
> Sunghwan Choi
> Ph.D candidate
> Computational Quantum Molecular Science Lab
> Department of Chemistry, KAIST, Republic of Korea
>
>
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