[Pw_forum] lattice instability and local minimum energy postion

[明文美]

Dear Prof. Paolo Giannozzi:
 
      yes, before I calculated phonon-dispersion of CrSb, I have followed your PRB paper several years ago concerning with phonon dispersion of semiconductors, Si, Ge,GaAs,GaSb,AlAs,AlSb,also using pw91-n-van.UPF pseudopotential ,and I found that I had to set the energy cutff and charge cutff larger than 40Ry and 500Ry respectively to get the correct frequencies consistent with your NC-LDA results,otherwise there will many imaginary frequencies for the acoustic branches . Therefore, in my CrSb case, I intentionally set the energy cutoff and charge cutff to be 60Ry and 600Ry, and also phonon scf-consisten threshold was set to be 10-16.
    Experimently, the bulk zinc-blende CrSb have not been synthesized and only CrSb in form of very film (about 2nm) exists experimentally. Thus I want to see whether the bulk CrSb is dynamically stable through phonon-dispersion calculation.
    Do I have to increase the energy cutoff to get a reliable phonon result ?
 
thanks very much !
 
Wenmei Ming > Date: Thu, 31 Jul 2008 17:13:26 +0200> From: giannozz at democritos.it> To: pw_forum at pwscf.org> Subject: Re: [Pw_forum] lattice instability and local minimum energy postion> > > > [...] I displaced atoms in the cell according > > to the eigen-displacements shown above,and got a cubic cell containg 8 > > atoms. But I found the energy rised with the increase of atom > > displacements, which was totally contrary to what I expected.> > have you tried the same operation on a simpler system, such as e.g.> GaAs? You should get the phonon frequencies. If you don't, you> may have made a mistake> > Paolo> -- > Paolo Giannozzi, Democritos and University of Udine, Italy> _______________________________________________> Pw_forum mailing list> Pw_forum at pwscf.org> http://www.democritos.it/mailman/listinfo/pw_forum
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