Hi,
What I could verify is that, in a simple test on rutile TiO2, I obtain
the same total energy (to within 10**(-7) Ry) with any of these lines in
the input file:
input_dft='sla+pw+tb09+tb09'
input_dft='pw+pbc+tb09+tb09'
input_dft="noc+nogc+tb09+tb09"
The first case is the one specified in the Modules/funct.f90 file as
equivalent to input_dft='tb09', the second one corresponds to having gga
correlation, the last one, to using no correlation at all. One can
understand this since the said file contains these lines:
! special case : TB09 meta-GGA Exc
else IF ('TB09'.EQ. TRIM(dftout) ) THEN
dft_defined = set_dft_values(0,0,0,0,0,3)
I think that since the original mBJ functional was defined as including
LDA correlation, this should be changed. Preferably, by allowing the
user to specify the type of correlation (s)he desires. I wonder if just
suppressing in the said file the three lines mentioned above would be
enough.
Regards,
JC Conesa
El 05/05/2018 a las 10:44, Paolo Giannozzi escribió:
I don't think it is possible right now to use any meta-GGA with
exchange/correlations/gradient corrections that differ from those
assumed in the original definition of the meta-GGA functional.
Meta-GGA follow a different path from all other XC functionals. I hope
to manage sooner or later to clean up the meta-GGA mess, but cannot
guarantee anything.
Paolo
On Fri, May 4, 2018 at 6:33 PM, José C. Conesa <jccon...@icp.csic.es
<mailto:jccon...@icp.csic.es>> wrote:
Hi,
Does this mean that it is not possible to combine tb09 with any
correlation contribution?
José Carlos
El 04/05/2018 a las 17:41, Paolo Giannozzi escribió:
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
<jccon...@icp.csic.es <mailto:jccon...@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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José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid, Spain
Tel. (+34)915854766
--
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
--
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Madrid, Spain
www.icp.csic.es
Tel. (+34)915854766
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