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cenwanglai榮譽版主 (知名作家)
老和山猥瑣派九段
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[求助]
請教:截斷能為什么是409這種奇怪的數(shù)字?為什么要交代未成對電子數(shù)Ns?
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看看這個交代計算的細節(jié)。ENCUT = 409 eV是如何得到的? Ns的設(shè)置是如何操作的,有什么意思? hehe.jpg[ Last edited by cenwanglai on 2012-9-22 at 16:46 ] |
榮譽版主 (知名作家)
老和山猥瑣派九段
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給作者發(fā)郵件問了,問題和回復(fù)如下: 1. Why the ENCUT = 409 eV is used? How dit you get the value 409? ENCUT=409eV corresponds to the cutoff used for Cl in the "hard" pseudopotential (Cl_h). If you looked for the keyword "ENMAX" into the POTCAR file corresponding to the hard Cl pseudopotential, you'll get: ENMAX = 409.136 To avoid comparing calculations obtained using different basis sets (e.i., different cutoff for the plane waves expension), we explicitly set ENCUT=409 in all the calculations including those not involving Cl (for instance the oxygen molecule in the gas phase). > 2. The number of unpaired electrons (Ns) was considered. How can you assign the Ns and fix it during geo optimaztion? Could you please show me the corresponding TAG in INCAR or other ways to make it? The number of unpaired electrons is fixed by the keyword "NUPDOWN". For instance "NUPDOWN=1" in the INCAR file means Ns=1 in the paper. The value of "NUPDOWN" appears in the "OSZICAR" and "out" files after each electronic minimization. Look at the number given after "mag" (for instance "mag= 0.0000" means "NUPDOWN = 0" . If you don't set thevalue of "NUPDOWN" in the INCAR file, VASP will compute the magnetization automatically. The problem with this approach is that the total magnetic moment may vary from one step to another during the geometry optimization. Personally, I prefer to fix NUPDOWN during the calculation and try different value of NUPDOWN. This ensure that I get the lowest "spin state" for a given geometry. Furthermore, this approach ensure the fulfilment of the "spin conservation" (see S. Chretien and H. Metiu J. Chem. Phys. 129(7), 074705 (2008)). |
榮譽版主 (知名作家)
老和山猥瑣派九段
榮譽版主 (著名寫手)
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1.“409”,很有可能是贗勢中的ENMAX或者ENMAX的1.3倍,也有可能是作者自己特意設(shè)置的這么個值。我覺得跟400或者450基本差別不大。 2.Ns是成單電子數(shù)目,關(guān)乎是否自旋極化、高低自旋態(tài)等。 個人理解,可以告知文獻出處么? |
木蟲 (正式寫手)
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因為VASP截斷半徑設(shè)置的單位是Ry 而它用的是15Ry, 1Ry=27.21eV, 15Ry=409eV |
木蟲 (著名寫手)
歷史控+原著控

榮譽版主 (著名寫手)
榮譽版主 (知名作家)
老和山猥瑣派九段
榮譽版主 (知名作家)
老和山猥瑣派九段
榮譽版主 (知名作家)
老和山猥瑣派九段
送鮮花一朵 |
謝謝回復(fù)。 郵件了作者,問題和回復(fù)已經(jīng)帖出來了。409是Cl的hard勢的ENMAX. VASP手冊上說: For some elements several PAW versions exist. The standard version has generally no extension. An extension _h implies that the potential is harder than the standard potential and hence requires a larger energy cutoff. The enxtension _s means that the potential is softer than the standard version. |
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