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cindywei

木虫 (初入文坛)

[求助] VASP计算稳定体系的零点能为什么也会出现虚频?

最近用VASP计算Gamma点的零点能做校正,原本热力学及力学上都能稳定存在的钯氢化合物有些成分点出现了虚频,是哪里出现问题了吗?
INCAR设置
ISTART = 0
ICHARG = 2
ENCUT = 450
ISMEAR = 0
PREC = A
EDIFF = 1E-6
EDIFFG = -0.001
NSW = 1
IBRION = 5
POTIM = 0.015
NFREE = 2

OUTCAR
1 f  =   20.970164 THz   131.759427 2PiTHz  699.489360 cm-1    86.725659 meV
2 f/i=   15.743741 THz    98.920841 2PiTHz  525.154652 cm-1    65.110902 meV
3 f/i=   15.775374 THz    99.119597 2PiTHz  526.209815 cm-1    65.241726 meV
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tider

木虫 (正式写手)

【答案】应助回帖

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franch: 金币+2, 谢谢回帖交流,, 2013-04-22 20:41:32
cindywei: 金币+5, ★★★很有帮助 2013-04-27 11:44:45
http://wolverton.northwestern.ed ... phonon-calculations

One drawback of the frozen-phonon method is that large supercells are needed to accurately calculate the force constant matrix. The periodic boundary conditions used in DFT calculations cause problems for the frozen phonon method. Displacing one atom in a small unit cell creates forces on all the atoms in the same unit cell, but also on the periodic images of these atoms.
2楼2013-04-18 10:59:53
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