[Pw_forum] vdw

[Dal Corso Andrea]

On Wed, 2009-09-09 at 16:53 +0700, Olga Sedelnikova wrote:
> Dear all,
> 
> I cannot find any documentation about vdw code. Please describe basic
> approaches used for polarizability calculations. 
> Examples 33 and 34 illustrates how to use ph.x and vdw.x to calculate
> polarizability of methane molecules. But results do not agree
> esecially for static value. Which method is better?

The two results should agree in the limit of large boxes. The reason is
that the results of vdw.x use the Clausius-Mossotti correction to speed
up the convergence of the calculated polarizability with the box size.
In the current 4.1 version, neither ph.x  nor phcg.x apply the
correction. This has been modified in cvs version of ph.x that now gives
a polarizability that agrees with the frequency dependent result at w=0.

HTH,

Andrea

See also Jour. of Chem. Phys. 120, 9934 (2004) for more details. 



> 
> Thank you,
> 
> Olga
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Andrea Dal Corso                    Tel. 0039-040-3787428
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