[QE-developers] Bug in xc_rVV10.f90

[Paolo Giannozzi]

Thank you for reporting this. I heard about this problem and discussed it
with Stefano dG who knows well that part of code. He thinks that the
current implementation is correct and that the discrepancy with respect to
analytical formulas is only apparent: in the limit |grad rho| =>0 it is
convenient to have a single diverging quantity (dq0_dgradrho) instead of
two (dq0_dgradrho and grad rho/mod_grad), or something like that

Paolo

On Wed, Apr 24, 2019 at 8:55 PM <tran at theochem.tuwien.ac.at> wrote:

> Hello,
>
> In xc_rVV10.f90, the formula for dq0_dgradrho (line 621) contains an error.
> Instead of
> dq0_dgradrho(i_grid) = dq0_dq  / ( 2.0_dp*k*w0 ) * 4.0_dp*wg2 /
> (mod_grad**2)
> this should be
> dq0_dgradrho(i_grid) = dq0_dq  / ( 2.0_dp*k*w0 ) * 4.0_dp*wg2 / mod_grad
>
> The authors of PBEsol+rVV10s
> https://journals.aps.org/prb/abstract/10.1103/PhysRevB.98.214108
> told me that they arrived at the same conclusion.
>
> Best regards,
>
> F. Tran (TU Wien)
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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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