[Pw_forum] how to obtain exchange energy and correlation energy separately?

[Paolo Giannozzi]

On Tue, Apr 12, 2016 at 2:54 PM, Uri Argaman <argamanu at post.bgu.ac.il>
wrote:

I wish to separate the "xc contribution" at the scf.out file into "exchange
> contribution" and "correlation contribution". What are you recommend?
> 1. to use the subroutine exxenergy2 from exx.f90 and substract the results
> from the "xc contribution"?
>

exxenergy2 compute "the Hartree-Fock exchange", not "the exchange
contribution" in "the exchange-correlation energy". Is this what you want?

2. to do something similar to what is written in v_of_rho.f90 for each of
> the contributions?
>
3. maybe something smarter?
>

it is not easy to disentangle the two contributions because they are
intertwined and you have to go quite deep into the code compute them
separately. The simplest way is I think to set to zero the correlation
terms (variables icorr, igcc in Modules/funct.f90) and recompute the energy
using v_of_rho

>
> I found similar question in the forum from 2014 with the answer that I
> have to modify the code.
>

this is still valid (and will always be, I think)

Paolo

thanks in advance,
>
> Uri Argaman
> Materials engineering department
> Ben-Gurion university
> Israel
>
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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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