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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