[Pw_forum] phonon frequencies are different when treated as insulator(semiconductor) and metal

[Paolo Giannozzi]

On Friday 07 January 2005 04:36, W. YU wrote:

> I am doing phonon dispersion calculations for a simple
> cubic system Cu3N. My band structure calculation has
> confirmed it is a semiconductor with a gap of about
> 0.15ev. [...] I still got different results when I treat it 
> differently as metal or as insulator(semiconductor).

>     occupations = 'smearing', degauss = 0.02 ,
>     smearing = 'methfessel-paxton'

the smearing "degauss" is in Rydberg (the documentation 
is not very clear on this point). With a gap of 0.15 eV and a 
broadening of 0.3 eV or so, your charge density will contain
some contribution from conduction bands, so there will be
some small differences with respect to the insulator case.

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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