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【原创】ecutwfc and ecutrho
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以下内容来自我的博客： blog.sina.com.cn/nkasir When I use PWgui to edit input file of pw.x, a warning always jumps out:"some variable are not set: List of unset variables: ecutrho". In my mind, in general plane wave code, only the energy cutoff for wavefunctions is adequate. Therefore, I never set ecutrho manually. This is the instruction of ecutrho:" Type: REAL Default: 4 * ecutwfc Description: kinetic energy cutoff (Ry) for charge density and potential May be larger ( for ultrasoft PP ) or somewhat smaller ( but not much smaller ) than the default value. Note that if you have norm-conserving PP only, setting it to a larger value than the default is a waste of time." But now, I know that it is only true for norm-conserving pseudopotentials, not for utral-soft ones. I find the following statement at: http://encina.northwestern.edu/i ... nd_PWSCF_in_general "We are going to use ultrasoft pseudopotentials here. In the case of norm-conserving pseudopotentials from Lab 2, ecutrho (the charge density cutoff) is automatically determined by 4*ecutwfc. However, in the case of ultrasoft pseudopotentials, we need an augmented charge around the ion core, so ecutrho should be higher than 4*ecutwfc. The usual value is 25-35 Ry for ecutwfc and 200-300 Ry for ecutrho. You might want to do a convergence check. Keep in mind that the value you should look at is the energy difference or force, not the absolute value of the energy (the energy will not converge unless you use very, very high ecutwfc and ecutrho). " [ Last edited by xirainbow on 2009-7-16 at 11:31 ] |
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freshgirl(金币+1,VIP+0):谢谢参与~ 7-17 14:13
wuchenwf(金币+2,VIP+0):谢谢分享 12-3 21:57
freshgirl(金币+1,VIP+0):谢谢参与~ 7-17 14:13
wuchenwf(金币+2,VIP+0):谢谢分享 12-3 21:57
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wuchenwf ，您好。 上面是在我学习ESPRESSO时被忽略的一个问题。 每次使用USP，我都采用了默认的ecutrho（既四倍的ecutwfc） 虽然GUI会提醒ecutrho没有设置，但是我没有做任何改动，直接计算。 后来才发现，norm-conserving时，ecutrho=4*ecutwfc是正确的设置 而USPS下，通常ecutrho=10*ecutwfc。而这个十倍是需要手动设置的 所以把自己的教训写在这里：） |
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