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[交流] 六角晶系結(jié)構(gòu)參數(shù)的優(yōu)化問題

由于初學(xué)VASP，不知道如何優(yōu)化六角晶系結(jié)構(gòu)參數(shù)，看侯老師講義上的內(nèi)容，還是不明白。真誠地希望各位高手們幫忙指教，謝謝！！

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1樓 2012-08-12 22:57:37

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奮力拼搏: 金幣+1 2012-08-15 19:44:18

這個(gè)不懂，只能來領(lǐng)金幣了

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9樓2012-08-13 07:10:47

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WDD880227: 金幣+1, 多謝提示 2012-08-13 19:07:31
奮力拼搏: 金幣+1 2012-08-15 19:39:17
奮力拼搏: 金幣+1 2012-08-15 19:44:26

樓主這問題和“vasp怎么用�。俊毙再|(zhì)差不多啊。。。。。你不說具體點(diǎn)，誰都沒辦法回答，只好灌水了
INCAR，事實(shí)上只要寫上ISIF=3，其他幾乎所有參數(shù)采用默認(rèn)值都不會(huì)有很大問題
KPOINTS注意用Gammacenter
POSCAR自己寫吧…………
暫時(shí)想到這么多

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22樓2012-08-13 15:23:31

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cclw

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WDD880227: 金幣+1, 多謝指教 2012-08-15 08:59:46
奮力拼搏: 金幣+1, 非常感謝您的回復(fù)，謝謝您��！ 2012-08-15 19:43:09

六角就兩個(gè)參數(shù)a和c，可以分別優(yōu)化。建議用a作為scale,先固定c/a，優(yōu)化a,直至能量最低；然后優(yōu)化c/a. 優(yōu)化的過程可以設(shè)isif=2查看stress,然后確定增大或減小參數(shù)。

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23樓2012-08-14 09:56:41

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WDD880227: 金幣+1, 多謝指教 2012-08-15 08:59:59
奮力拼搏: 金幣+1, 謝謝您的回復(fù)！ 2012-08-15 19:43:53

用isif=3就是簡單優(yōu)化
可以先把精度設(shè)置低一些（prec、ecut、k-mesh這些參數(shù)）
然后逐漸提高精度直至收斂

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25樓2012-08-14 20:04:31

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引用回帖:

23樓: Originally posted by cclw at 2012-08-14 09:56:41
六角就兩個(gè)參數(shù)a和c，可以分別優(yōu)化。建議用a作為scale,先固定c/a，優(yōu)化a,直至能量最低；然后優(yōu)化c/a. 優(yōu)化的過程可以設(shè)isif=2查看stress,然后確定增大或減小參數(shù)。

麻煩您給我細(xì)講一下怎樣做才能固定c/a優(yōu)化a,能量最低之后又怎樣做才能優(yōu)化c/a呢？
麻煩您給我講一下吧，謝謝

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27樓2012-08-15 19:42:43

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WDD880227: 金幣+1, 多謝指教 2012-08-17 08:43:59
奮力拼搏: 金幣+3, 非常感謝您的回復(fù)！！謝謝！1 2012-08-19 17:39:42

看你對(duì)精度有啥要求，如果要求不是太高的話，直接設(shè)置ISIF=3，弛豫就可，最后的結(jié)構(gòu)就是優(yōu)化后的結(jié)果

如果要求精度較高，就得做V-E曲線，vasp manual上的：
Accurate bulk relaxations with internal parameters (one)

The general message is: whenever possible avoid volume relaxation with the default energy cutoff. Either increase the basis set by setting ENCUT manually in the INCAR file, or use method two suggested below, which avoids doing volume relaxations at all. If volume relaxations are the only possible and feasible option please use the following step by step procedure (which minimizes errors to a minimum):

Relax from starting structure (ISMEAR should be 0 or 1, see section 6.38).
Start a second relaxation from previous CONTCAR file (re-relaxation).
As a final step perform one more energy calculation with the tetrahedron method switched on (i.e. ISMEAR=-5), to get very accurate and unambiguous energies (no relaxation for the final run). The final calculation should be done with PREC=High, to get very accurate energies.
A few things should be remarked here: Never take the energy obtained at the end of a relaxation run, if you allow for cell shape relaxations (the final basis set might not be isotropic). Instead perform one additional static run at the end.
The relaxation will give a structure which is correct to first order, the final error in the energy of step 3 is of second order (with respect to the structural errors). If you take the energy directly from the relaxation run, errors are usually significantly larger. Another important point is that the most accurate results for the relaxation will be obtained if the starting cell parameters are very close to the final cell parameters. If different runs yield different results, then the run which started from the configuration which was closest to the relaxed structure, is the most reliable one.

We strongly recommend to do any volume (and to lesser extend cell shape) relaxation with an increased basis set. ENCUT=1.3 default cutoff is reasonable accurate in most cases. PREC=High does also increase the energy cutoff by a factor 1.25. At an increased cutoff the Pulay stress correction are usually not required.

Accurate bulk relaxations with internal parameters (two)

It is possible to avoid volume relaxation in many cases: The method we have used quite often in the past, is to relax the structure (cell shape and internal parameters) for a set of fixed volumes (ISIF=4). The final equilibrium volume and the groundstate energy can be obtained by a fit to an equation of state. The reason why this method is better than volume relaxation is that the Pulay stress is almost isotropic, and thus adds only a constant value to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will give an almost correct structure.

The outline for such a calculation is almost the same as in the previous section. But in this case, one has to do the calculations for a set of fixed volumes. At first sight this seems to be much more expensive than method number one (outlined in the previous section). But in many cases the additional costs are only small, because the internal parameters do not change very much from volume to volume.

Select one volume and relax from starting structure keeping the volume fixed (ISIF=4 see sec. 6.24; ISMEAR=0 or 1, see section 6.38).
Start a second relaxation from previous CONTCAR file (if the initial cell shape was reasonable this step can be skipped, if the cell shape is kept fixed, you never have run VASP twice).
As a final step perform one more energy calculation with the tetrahedron method switched on (ISMEAR=-5), to get very accurate unambiguous energies (no relaxation for the final run).
The method has also other advantages, for instance the bulk modulus is readily available. We have found in the past that this method can be used safely with the default cutoff. (see also section 9.2).

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[考研] 求調(diào)劑 +3	.m.. 2026-03-21	4/200	2026-03-21 16:25 by barlinike
[考研] 0805材料320求調(diào)劑 +3	深海物語 2026-03-20	3/150	2026-03-21 15:46 by 無際的草原
[考研] 332求調(diào)劑 +3	鳳凰院丁真 2026-03-20	3/150	2026-03-21 10:27 by luoyongfeng
[考研] 265求調(diào)劑 +3	Jack?k?y 2026-03-17	3/150	2026-03-21 03:17 by JourneyLucky
[考研] 化學(xué)求調(diào)劑 +4	臨澤境llllll 2026-03-17	5/250	2026-03-21 02:23 by JourneyLucky
[考研] 354求調(diào)劑 +5	Tyoumou 2026-03-18	8/400	2026-03-21 00:35 by JourneyLucky
[考研] 274求調(diào)劑 +10	S.H1 2026-03-18	10/500	2026-03-20 23:51 by JourneyLucky
[考研] 一志愿中海洋材料工程專碩330分求調(diào)劑 +8	小材化本科 2026-03-18	8/400	2026-03-20 23:16 by JourneyLucky
[考研] 求調(diào)劑，一志愿:南京航空航天大學(xué)大學(xué) ，080500材料科學(xué)與工程學(xué)碩，總分289分 +4	@taotao 2026-03-19	4/200	2026-03-20 22:14 by JourneyLucky
[考研] 085600材料與化工 +8	安全上岸！ 2026-03-16	8/400	2026-03-20 22:13 by luoyongfeng
[考研] 中南大學(xué)化學(xué)學(xué)碩337求調(diào)劑 +3	niko- 2026-03-19	6/300	2026-03-20 21:58 by luoyongfeng
[考研] A區(qū)線材料學(xué)調(diào)劑 +5	周周無極 2026-03-20	5/250	2026-03-20 21:33 by laoshidan
[考研] 289求調(diào)劑 +6	懷瑾握瑜l 2026-03-20	6/300	2026-03-20 20:30 by 學(xué)員8dgXkO
[論文投稿] 申請(qǐng)回稿延期一個(gè)月，編輯同意了。但系統(tǒng)上的時(shí)間沒變，給編輯又寫郵件了，沒回復(fù) 10+3	wangf9518 2026-03-17	4/200	2026-03-19 23:55 by babero
[考研] 320求調(diào)劑0856 +3	不想起名字112 2026-03-19	3/150	2026-03-19 22:53 by 學(xué)員8dgXkO
[考研] 材料考研調(diào)劑 +3	xwt。 2026-03-19	3/150	2026-03-19 11:22 by w沐陽w
[考研] 一志愿985，本科211，0817化學(xué)工程與技術(shù)319求調(diào)劑 +10	Liwangman 2026-03-15	10/500	2026-03-19 10:25 by 無際的草原
[考研] 311求調(diào)劑 +6	26研0 2026-03-15	6/300	2026-03-18 14:43 by haxia
[考研] 070300化學(xué)學(xué)碩求調(diào)劑 +6	太想進(jìn)步了0608 2026-03-16	6/300	2026-03-16 16:13 by kykm678
[考研] 070303 總分349求調(diào)劑 +3	LJY9966 2026-03-15	5/250	2026-03-16 14:24 by xwxstudy

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