[QE-users] on the use of tb09 functional from libxc

[Paolo Giannozzi]

I think that with meta-GGA what is written in the first two fields is just
ignored

Paolo

On Fri, May 4, 2018 at 5:39 PM, José C. Conesa <jcconesa at icp.csic.es> wrote:

> Dear QE developers,
>
> I wish to use in Quantum Espresso the tb09 potential-only meta-GGA
> functional (from Tran & Blaha, PRL 102, 2009, 226401) which is available in
> libxc. I downloaded the libxc library and compiled successfully qe-6.2.1
> with it. Then I see in Modules/funct.f90 that the instruction to use this
> functional is equivalent to specifying
>
> input_dft="sla+pw+tb09+tb09"
>
> But as far as I know, the tb09 functional gives only the exchange part,
> and gives it in full (not as a correction to another expression for the
> exchange), while sla is a LDA exchange form (and pw a LDA correlation
> form). Should one conclude that exchange is being introduced twice? And, is
> a gradient correction to the correlation term not included? From these
> considerations, I would have thought that using something like
>
> input_dft="pw+pbc+tb09+tb09"
>
> (where I hope that the tb09 exchange functional is not included twice),
> i.e. the correlation part of PBE plus the Tran & Blaha exchange functional,
> would be the proper way to proceed.
>
> Can you please comment on this?
>
> I also would add that it would be good to be able to adjust the A and B
> parameters of the tb09 functional. This has been proposed in (Koller, Tran
> & Blaha, PRB 85, 2012, 155109) to obtain better bandgaps in certain
> families of semiconductors.
>
> All the best,
>
> --
> José C. Conesa
> Instituto de Catálisis y Petroleoquímica, CSIC
> Marie Curie 2, Cantoblanco
> 28049 Madrid, Spain
> Tel. (+34)915854766
>
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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