Hi Marcos
It is a semi-local potential, with an orbital independent exchange-correlation
potential which depends solely on semi-local quantities. It constructs the
xc-potential with the modified Becke-Johnson for the exchange-potential part
and uses LDA correlation potential part. All of this constitutes a modified
potential XC-potential, but it is not a XC-energy functional. For this reason
the Exc is taken from PBE and the forces obtained that cannot be used with this
option.
As a summary, it is used at the end of normal volumen-coordinates optimization
procedure, after obtaining a converged calculation then you proceed to a last
SCF where the exchange-potential and correlation-potential is modified,
correcting the band gap in a single-point.
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: [email protected]
Phone: 598 2 924 98 59
598 2 929 06 48
Fax: 598 2 9241906
Web: http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
---------------------------------------------------------------------------------
----- Original Message -----
From: Marcos Veríssimo Alves
To: [email protected]
Sent: Tuesday, June 15, 2010 1:44 PM
Subject: Re: [SIESTA-L] Band Gap Help
Hola Ricardo,
Normally I'd go search for the reference but right now I'm busy as hell...
So, two questions:
1) "x-potential" would refer to the exchange part of the exchange and
correlation potential?
2) Is it a hybrid functional?
Cheers,
Marcos
On Tue, Jun 15, 2010 at 6:38 PM, Ricardo Faccio <[email protected]> wrote:
A short comment GAPS
Recently Trand & Blaha PRL 102, 226401 (2009) presented a modified
version of the x-potential proposed by Becke & Johnson [J. Chem. Phys. (2006)]
calculating band gaps for solids with an accuracy similar to GW and
Experiments. This new flavor have been recently added to the new version WIEN2k.
I fastly tested rutile and antase, finding Egap= 2.73 eV and 3.04 eV
respectively
It is efficient and parameter free (in difference to DFT+U).
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: [email protected]
Phone: 598 2 924 98 59
598 2 929 06 48
Fax: 598 2 9241906
Web: http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
---------------------------------------------------------------------------------
----- Original Message ----- From: Marcos Veríssimo Alves
To: [email protected]
Sent: Tuesday, June 15, 2010 1:25 PM
Subject: Re: [SIESTA-L] Band Gap Help
Robert,
Rutile is a widely studied system, so there should be accurate plane-wave
calculation in the literature for you to compare your result. LDA can indeed
seriously underestimate band gaps, and even render insulators metallic
sometimes. I recommend you do a search in the literature and see if other PW or
Siesta/local orbital calculations yield the same result.
Marcos
On Tue, Jun 15, 2010 at 6:18 PM, Koch, Robert J <[email protected]> wrote:
Hello All,
I'd greatly appreciate any advice on the following:
I'm trying to calculate the band gap of TIO2 (Rutile). I have attached my
fdf file, my pseudo .psf files as well as their input .inp files.
When I run this and use the eig2dos utility to plot density of states, I
see a band gap of about 1.4 eV which is far too low (should be about 3.3 eV).
I'm aware that typically DFT calculations underestimate the band gap, but this
underestimation seems like a little much. Can anyone make any recemendations
as to how to improve my calculation? I'm quite stuck and not sure how to
proceed.
Thanks in advance!
Rob Koch
