[Pw_forum] 3rd Order Properties and GGA's

[Paolo Giannozzi]

John Kendrick wrote:
> 
> I have recently been looking at calculating Raman scattering intensities
> at q=0 for organic crystals.  I was aware that ultra soft potentials are
> not supported for the calculation of 3rd order properties.  I recently
> tried out the CVS version of Quantum Espresso and discovered that there
> is a check in phq_setup.f90 that aborts the calculation if the density
> functional is a GGA.  No such check exists in 4.0.1.

the problem is that the calculation of third derivatives wrt the
charge density of the exchange-correlation energy was never
implemented. Only the LDA part is calculated, and only for the
Perdew-Zunger parameterization. I do not expect this to introduce
a big error, though, so you might try (at your own risk) to
comment out that check

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