[Wien] New exchange-correlation potential

[Ricardo Faccio]

Dear F. Tran
What about the use of total energy for: Volume cell optimization and/or for 
evaluation of a particular magnetic arrangement ? Can it be used for 
comparative purposes? or the procedure indicates that we need to optimize 
everything first (forces and volume) for a particular "variational" 
xc-potentinal (eg. PBE, etc) and then proceed with MBJ by doing a single 
point?
Best regards
Ricardo
-------------------------------------------------------------------------
  Dr. Ricardo Faccio
  Prof. Adjunto de Física
  Mail: Cryssmat-Lab., Cátedra de Física, DETEMA
  Facultad de Química, Universidad de la República
       Av. Gral. Flores 2124, C.C. 1157
       C.P. 11800, Montevideo, Uruguay.
  E-mail: rfaccio at fq.edu.uy
  Phone: 598 2 924 98 59
              598 2 929 06 48
  Fax:    598 2 9241906
  Web:  http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
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----- Original Message ----- 
From: "F. Tran" <tran at theochem.tuwien.ac.at>
To: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
Sent: Wednesday, June 09, 2010 6:54 PM
Subject: Re: [Wien] New exchange-correlation potential


> Hello,
>
> In order to use the modified Becke-Johnson exchange potential
> you have to choose indxc=28 in case.in0 and indxc=50 in case.in0_grr.
>
> A few more things:
>
> In case.in0 you also need to replace NR2V by R2V such that the
> exchange-correlation potential is written in case.r2v, which will
> be used in the next iteration.
>
> You need case.inm_vresp such that case.vrespsum (which contains a
> part of the kinetic-energy density) is created.
>
> There is no adjustable parameters.
>
> The LDA correlation potential is added to the MBJ exchange potential.
>
> The LDA exchange-correlation functional is used for the energy.
>
> The MBJ exchange potential is not the derivative of an energy functional,
> which means that the method is not variational (i.e., the orbitals are
> not the ones which minimize the total energy, which is LDA).
> In particular, it means that you can not use forces to optimize internal
> parameters.
>
>
> On Wed, 9 Jun 2010, yhzhao wrote:
>
>> Dear Prof. Pblaha,
>>
>> I have tried to calculate something using the new exchange potential
>> with indxc=50 as suggested by the usersguide. At first I want to repeat
>> some data given by PRL 102, 226401 (2009), for example, the band gap of
>> GaAs. I can get a band gap of 0.7 eV for GaAs, which is much better than
>> 0.3 eV of lda, but not much better than the value given by you in PRL
>> 102, 226401 (2009). In the calculation, I use the experimental lattice
>> constant. The k-grid have been increased as dense as 20x20x20 and RKmax
>> as large as 9.0.
>>
>> Is there any adjustable parameter for the MBJ calculation? Thanks.
>>
>> Regards,
>>
>> yonghong
>>
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