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 thataborts 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

http://www.democritos.it/pipermail/pw_forum/2008-September/010123.html

 

 

 

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

http://www.democritos.it/pipermail/pw_forum/2010-February/015918.html

 

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