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Dear Prof. Paolo Giannozzi:<BR>
<BR>
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.<BR>
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.<BR>
Do I have to increase the energy cutoff to get a reliable phonon result ?<BR>
<BR>
thanks very much !<BR>
<BR>
Wenmei Ming <BR><BR>> Date: Thu, 31 Jul 2008 17:13:26 +0200<BR>> From: giannozz@democritos.it<BR>> To: pw_forum@pwscf.org<BR>> Subject: Re: [Pw_forum] lattice instability and local minimum energy postion<BR>> <BR>> <BR>> > [...] I displaced atoms in the cell according <BR>> > to the eigen-displacements shown above,and got a cubic cell containg 8 <BR>> > atoms. But I found the energy rised with the increase of atom <BR>> > displacements, which was totally contrary to what I expected.<BR>> <BR>> have you tried the same operation on a simpler system, such as e.g.<BR>> GaAs? You should get the phonon frequencies. If you don't, you<BR>> may have made a mistake<BR>> <BR>> Paolo<BR>> -- <BR>> Paolo Giannozzi, Democritos and University of Udine, Italy<BR>> _______________________________________________<BR>> Pw_forum mailing list<BR>> Pw_forum@pwscf.org<BR>> http://www.democritos.it/mailman/listinfo/pw_forum<BR><BR><br /><hr />轻松把Hotmail下载到本地，试试 Windows Live Mail。 <a href='http://get.live.com/wl/all' target='_new'>立即尝试！</a></body>
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