[Pw_forum] Re: finite electric field method (li niu)

umari at democritos.it umari at democritos.it
Wed May 23 19:14:11 CEST 2007

> Dear PaoloU,

> Thanks for your help. I still have several questions to consult you.
> 1.Is it suitable to calculate Raman spectrum of tetrahedral amorphous 
> carbon >using the finite electric method?

Yes, it is (in the nonresonant limit)  and should be not particularly 
demanding in terms of
computational resources. You can follow the methods described in
Diamond and related materials, 14, 1255 (2005).

> 2.You said that atomic forces and electric fields are implemented for the US
> pseudopotentials only in the cp code ,but I found they may be 
> implemented for >NC pseudopotentials for tetrahedral amorphous 
> carbon. Why is it?

forces for NC pseudopotential plus electric field do not require additional
terms and are correctly calculated both in cp and pw

> 3.Using ph.x to calculate the phonon frequencies and eigenmodes and 
> cp.x to >calculate Raman susceptibilities by finite electric method, 
> is it feasible?

Yes it is but you could also calculate directly the Raman spectrum 
using the 2n+1 theorem which is implemented with pw and phonon


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