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xirainbow木虫 (正式写手)
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【分享】Convergence tests
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以下内容来自我的博客：blog.sina.com.cn/nkasir I have never tried convergence test, although I knew it for a long time. I find some intereting test, and put it here  [ Last edited by xirainbow on 2009-8-2 at 09:41 ] |
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xirainbow
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4楼2009-09-20 17:40:05
xirainbow
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fegg7502(金币-2,VIP+0):thank you very much! 9-20 16:28
fegg7502(金币+4,VIP+0):thank you very much! 9-20 16:46
fegg7502(金币-2,VIP+0):thank you very much! 9-20 16:28
fegg7502(金币+4,VIP+0):thank you very much! 9-20 16:46
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内容来源：http://blog.sina.com.cn/s/blog_5f15ead20100d1ki.html The cut-off radius for Kohn-Sham orbitals, G_cut, is usually defined in terms of its corresponding kinetic energy, E_cut: G_cut=(2*E_cut)^0.5 The cut-off radius for densities and potentials should be double that for orbitals. The cut-off energy that is appropriate for a given calculation is not usually known in advance, as it depends very much on the system in question, and on which quantities one wishes to calculate. However, establishing what the appropriate cut-off energy is essentially just a matter of increasing it until the result stops changing - a procedure known as a convergence test. This feature of a plane wave basis set - i.e. that its accuracy can be controlled by a single parameter - is a major advantage over, for example, localised basis sets. One can usually be quite confident, once a result is converged with respect to the cut-off energy, that there is no unrepresented Hilbert space that would significantly affect that result.It is however, important to bear in mind that quantities related to derivatives of the energy, such as force and stress, may require a slightly higher cut off energy than the energy itself, depending on the desired accuracy. (2009-09-20) |
2楼2009-09-20 09:46:23
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3楼2009-09-20 16:46:33