[Wien] New exchange-correlation potential

[sudhir kumar]

Dear user,
did you able to improve band gap of gaas with new Xc.
kumar


--- On Thu, 10/6/10, yhzhao <yhzhao.mail at gmail.com> wrote:


From: yhzhao <yhzhao.mail at gmail.com>
Subject: Re: [Wien] New exchange-correlation potential
To: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
Date: Thursday, 10 June, 2010, 18:29


Hello,

I have got a band gap of 0.8 eV, with lattice constant 5.6533 Angstrom and the space group No. is 216, with two atoms in (0.0 0.0 0.0) and (0.25 0.25 0.25).

I have checked that:

1. In GaAs.inm_vresp, YES has been replaced by NO;
2. I have done the calculation as following steps:
    For the first scf run, I have set NR2V and indxc=5 in GaAs.in0;
    Change NR2V to R2V and run one more scf cycle; 
    save lda;
    Set indxc=28 in GaAs.in0;
    cp GaAs.in0 GaAs.in0_grr and set index=50 in GaAs.in0_grr
    run_lapw -p -cc 0.00001
    plot bandstructure

Anything wrong with my procedure? 

yonghong
On 2010年06月10日 05:06, F. Tran wrote: 

Which value do you obtain? Did you use the correct structure?
In Table 1 of the following paper:
Tran et al., J. Phys.: Condens. Matter 19, 196208 (2007)
it is indicated which structure and lattice constant were used.

In case.inm_vresp, you have to replace YES by NO for the normalization.


On Wed, 9 Jun 2010, yhzhao wrote:

  
Hi,
I have do all your suggested things, which given in the usersguide. However I
cannot get the band gap, that is 1.64 eV for GaAs, as suggested by PRL 102,
226401 (2009).


yonghong
On 2010年06月09日 17:54, F. Tran wrote:
    
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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