[Pw_forum] error in ph( ir and raman spectrum)

[Paolo Giannozzi]

Carlos Reis wrote:

> from phq_setup : error #         1
>      third order derivatives not implemented with GGA
> 
> Any idea why this shows up in 4.1.2 and not on 4.0.3. Does 4.0.3 have a bug?

yes and no: it was calculating third-order energy derivatives in GGA
using the LDA expression for
   \delta^3 E_{xc}/\delta n(r')\delta n(r')\delta n(r")
Maybe not a big deal, because this terms seems to give a rather small
contribution, but it is not the correct espression. You can comment
out the check and you will get the same numbers as before

P.
-- 
Paolo Giannozzi, Democritos and University of Udine, Italy