[Wien] A basic question regarding the band structure

[shamik chakrabarti]

Dear Wien2k users,

We have transformed a material with FCC space group
symmetry to primitive lattice by forming a supercell in order to
incorporate the substitution of an element partially.

*Our query is:* when we are trying to plot band structure, we are getting
the special symmetric points corresponding to simple cubic symmetry
while not getting the special points corresponding to FCC symmetry.

In this regard, while the plotted band structure is correct or wrong? If
its wrong what is the remedy.

Thanks in advance.

with regards,

-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] Ghost band error

[shamik chakrabarti]

Dear Prof. Gavin,

The problem is solved by changing Rmt of P to 1.45.

Thank you so much!

with regards,

On Sat, 18 Sept 2021 at 20:27, Gavin Abo  wrote:

> You might want to check what value you used for -ecut as I noticed a
> WARNING from lstart of WIEN2k 21.1 if the default value of -6.0 is used:
>
> username@computername:~/Desktop/test/LFP_opt$ ls
> LFP_opt.struct
> username@computername:~/Desktop/test/LFP_opt$ init_lapw -b -ecut -6.0
> ...
>  next is lstart
>   SELECT XCPOT:
>   recommended: PBE[(13) GGA of Perdew-Burke-Ernzerhof 96]
>LDA[( 5)]
>WC [(11)  GGA of Wu-Cohen 2006]
>PBESOL [(19) GGA of Perdew etal. 2008]
>   SELECT ENERGY to separate core and valence states:
>   recommended: -6.0 Ry (check how much core charge leaks out of MT-sphere)
>   ALTERNATIVELY: specify charge localization (between 0.97 and 1.0) to
> select core state
> STOP LSTART ENDS
> WARNING:   0.057 PCORE electrons leak out of MT-sphere 
> :WARNING: 0.057  PCORE electrons leak out of MT-sphere 
> :WARNING: touch .lcore and run scf-cycle with core density superposition
> :WARNING: Or: rerun lstart with lower E-core separation energy
> :WARNING: ORBITAL:  2P*-9.172-9.141
> :WARNING: ORBITAL:  2P -9.104-9.074
>  file .lcore created, scf-cycle with core-density superposition !
> ...
>
> I see that your struct has P and O atoms.  The ghostbands error your
> encountering might be a common problem with struct files having those
> atoms.  You might want to search past posts to see if they can help with
> that such as at the two links:
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20276.html
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg18031.html
>
> On 9/18/2021 4:37 AM, shamik chakrabarti wrote:
>
> Dear Wien2k users,
>
>  I want to run a volume optimization for LiFePO4. However,
> at the first iteration it shows a Ghost Band error. I have attached the
> struct file (both initial & -2% decreased volume struct) herewith this mail.
>
> Thanks in advance.
>
> with regards,
>
> --
> Dr. Shamik Chakrabarti
> Research Fellow
> Department of Physics
> Indian Institute of Technology Patna
> Bihta-801103
> Patna
> Bihar, India
>
> ___
> Wien mailing list
> Wien@zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>


-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] Ghost band error

[Gavin Abo]

You might want to check what value you used for -ecut as I noticed a 
WARNING from lstart of WIEN2k 21.1 if the default value of -6.0 is used:


username@computername:~/Desktop/test/LFP_opt$ ls
LFP_opt.struct
username@computername:~/Desktop/test/LFP_opt$ init_lapw -b -ecut -6.0
...
 next is lstart
  SELECT XCPOT:
  recommended: PBE    [(13) GGA of Perdew-Burke-Ernzerhof 96]
   LDA    [( 5)]
   WC [(11)  GGA of Wu-Cohen 2006]
   PBESOL [(19) GGA of Perdew etal. 2008]
  SELECT ENERGY to separate core and valence states:
  recommended: -6.0 Ry (check how much core charge leaks out of MT-sphere)
  ALTERNATIVELY: specify charge localization (between 0.97 and 1.0) to 
select core state

STOP LSTART ENDS
WARNING:   0.057 P    CORE electrons leak out of MT-sphere 
:WARNING: 0.057  P    CORE electrons leak out of MT-sphere 
:WARNING: touch .lcore and run scf-cycle with core density superposition
:WARNING: Or: rerun lstart with lower E-core separation energy
:WARNING: ORBITAL:  2P*    -9.172    -9.141
:WARNING: ORBITAL:  2P -9.104    -9.074
 file .lcore created, scf-cycle with core-density superposition !
...

I see that your struct has P and O atoms.  The ghostbands error your 
encountering might be a common problem with struct files having those 
atoms.  You might want to search past posts to see if they can help with 
that such as at the two links:


https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20276.html
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg18031.html

On 9/18/2021 4:37 AM, shamik chakrabarti wrote:

Dear Wien2k users,

 I want to run a volume optimization for LiFePO4. 
However, at the first iteration it shows a Ghost Band error. I have 
attached the struct file (both initial & -2% decreased volume struct) 
herewith this mail.


Thanks in advance.

with regards,

--
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

[Wien] Ghost band error

[shamik chakrabarti]

Dear Wien2k users,

 I want to run a volume optimization for LiFePO4. However,
at the first iteration it shows a Ghost Band error. I have attached the
struct file (both initial & -2% decreased volume struct) herewith this mail.

Thanks in advance.

with regards,

-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India


LFP_opt.struct
Description: Binary data


LFP_opt_initial.struct
Description: Binary data
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] query for elastic constants

[Peter Blaha]

The most fundamental procedure is to use the theoretically optimized 
volume for all properties.
If the DFT result is very bad, sometimes one also used experimental 
lattice parameters.


Phonons: There is nothing unusual about imaginary phonons in the 
harmonic approximation for cubic perovskites. Your calculations are at 
T=0 and most cubic perovskites are unstable at low temperature and show 
one (or even more)  phase transitions when T is lowered.


In principle, one can do anharmonic phonons, which allows to calculated 
phonons at finite temperature and then obtain a free energy. This way 
you can get lattice parameters at finite temp. as well as phase 
transition temperatures.

see eg. PHYSICAL REVIEW B 103, 094108 (2021)

Am 17.09.2021 um 13:52 schrieb fatima DFT:

Dear Sir,
I understand your point.  I am using PBE functional.

I am still in doubt, which lattice parameter I should use for the rest 
of the properties.

Thanks


On Fri, Sep 17, 2021 at 5:11 PM Laurence Marks > wrote:


That means that the cubic phase is not stable at T=0 for the
functional you have chosen. This may be correct or incorrect, it is
not uncommon (e.g. SrTiO3 with PBE).

_
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what
nobody else has thought", Albert Szent-Györgyi
www.numis.northwestern.edu 

On Fri, Sep 17, 2021, 06:37 fatima DFT mailto:fatimad...@gmail.com>> wrote:

Thanks Sir
No Sir!!!
I mean, the original system is lower in energy but the phonon
band structure has some soft modes.
When I apply a compressive strain, the soft mode disappears.
I am sorry if you found my previous query a bit confusing.

Thanks
Fatima



On Fri, Sep 17, 2021 at 5:01 PM Laurence Marks
mailto:laurence.ma...@gmail.com>> wrote:

If I understand you correctly, your system is lower in
energy for a slightly smaller lattice parameter. This is not
unusual, and depends upon what functional you use. It is
standard to calculate using the cell parameters that
minimize the dft energy.

Is this right? What is the relevance of "right"? Doing
phonons for a non dft-equilibrium cell is obvious GIGO.
Beyond that to band etc there is no "right".

_
Professor Laurence Marks
"Research is to see what everybody else has seen, and to
think what nobody else has thought", Albert Szent-Györgyi
www.numis.northwestern.edu 

On Fri, Sep 17, 2021, 06:22 fatima DFT mailto:fatimad...@gmail.com>> wrote:

I want to extend my question for band, doss, optical
properties as well.

One important thing is that the total energy is more
negative for the original system by 0.65 eV when I apply
2.5% compressive strain and 2.8 eV when I apply 5%
compressive strain.

Thanks


On Fri, Sep 17, 2021 at 3:33 PM fatima DFT
mailto:fatimad...@gmail.com>> wrote:

Dear All,

I am dealing with a cubic 3D perovskite system.
With its original lattice parameters, the system
shows negative frequencies.
At some 1% lattice strain, the system becomes
dynamically stable (no +ve frequency).

My question is: Should I calculate elastic constant
at the lattice parameters where the system is
dynamically stable or should I consider the case
with its original lattice parameters (fully
optimized geometry with no strain)?


Thank you
Fatima

___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at


https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!CU-q4QLnagFyEv62yxcAvl8Kfi5TLM-08F260z_aYMEY99K8U8ECAO3K3s3jWBg6hGRtqQ$



SEARCH the MAILING-LIST at:

https://urldefense.com/v3/__http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html__;!!Dq0X2DkFhyF93HkjWTBQKhk!CU-q4QLnagFyEv62yxcAvl8Kfi5TLM-08F260z_aYMEY99K8U8ECAO3K3s3jWBiYk8FZEA$