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【求助】對(duì)于難收斂的體系 已有6人參與
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| 各位,對(duì)于vasp優(yōu)化難收斂的體系,可不可以這樣做,先用低的收斂標(biāo)準(zhǔn)使其收斂,然后讀入波函數(shù)和電荷再采用高的收斂標(biāo)準(zhǔn)進(jìn)行計(jì)算,可行否?多謝指教! |
VASP優(yōu)化不收斂 |
捐助貴賓 (正式寫(xiě)手)
木蟲(chóng) (正式寫(xiě)手)
Dr.

榮譽(yù)版主 (知名作家)
老和山猥瑣派九段
木蟲(chóng) (正式寫(xiě)手)
Dr.
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如果已經(jīng)開(kāi)始弛豫了好幾步了,就copy過(guò)來(lái),如果第一步都沒(méi)過(guò)去,那就不必了。 收斂參數(shù)的調(diào)整量子化學(xué)論壇以前有個(gè)老帖 你自己看看有沒(méi)有你能用的 對(duì)于一些磁性體系、鑭系和錒系元素及相關(guān)化合物的靜態(tài)計(jì)算(電子迭代),經(jīng)常會(huì)遇到“難收斂”的問(wèn)題。 下面給出幾個(gè)相關(guān)Flag及設(shè)置方法:(有些話從說(shuō)明書(shū)上摘錄的,不大好翻譯,就copy了,請(qǐng)見(jiàn)諒) 1、LMAXMIX Default: LMAXMIX = 2 An additional flag controls up to which l quantum number the onsite PAW charge densities are passed through the charge density mixer. Higher l-quantum numbers are usually not handled by the mixer. In order to obtain fast convergence to the groundstate, you can try the following setting: LMAXMIX = 4 for d elements LMAXMIX = 6 for f elements 這個(gè)FLAG對(duì)于含d電子和f電子的體系是非常重要的,很大一部分體系的收斂問(wèn)題可以通過(guò)設(shè)置合適的LMAXMIX值來(lái)解決。 2、ALGO, IALGO, LDIAG If the self-consistency loop does not converge within 40 steps, it will probably not converge at all. In this case you should reconsider the tags IALGO, LDIAG, and the mixing-parameters. 這是說(shuō)明書(shū)上的建議。 一般情況下,或使用IALGO=48時(shí)遇到收斂問(wèn)題的話,可以考慮設(shè)IALGO為38(4.5以前的版本可設(shè)為8),或設(shè)置ALGO=Normal or Fast (in VASP.4.5 and later versions)。 3、NELMDL NELMDL gives the number of non-selfconsistent steps at the beginning; if one initializes the wave functions randomly the initial wave functions are far from anything reasonable. The resulting charge density is also 'nonsense'. Therefore it makes sense to keep the initial Hamiltonian, which corresponds to the superposition of atomic charge densities, fixed during the first few steps. Choosing a 'delay' for starting the charge density update becomes essential in all cases where the SC-convergence is very bad (e.g. surfaces or molecules/clusters chains). Without setting a delay VASP will probably not converge or at least the convergence speed is slowed down. NELMDL might be positive or negative. A positive number means that a delay is applied after each ionic movement -- in general not a convenient option. A negative value results in a delay only for the start-configuration. 4、mixing-parameters 對(duì)于一些難收斂的體系,可以使用“l(fā)inear mixing”,具體詳見(jiàn)VASP說(shuō)明書(shū)中的“Mixing-tags”。 For an initial linear mixing (BMIX ~ 0) an optimal setting for A(AMIX) can be found easily by setting Aopt=Acurrent*Γmean. For the Kerker scheme either A or q0(i.e. AMIX or BMIX) can be optimized, but we recommend to change only BMIX and keep AMIX fixed (you must decrease BMIX if the mean eigenvalue is larger than one, and increase BMIX if the mean eigenvalue is smaller than one). 盡管VASP說(shuō)明書(shū)中給出了調(diào)節(jié)AMIX和BMIX的一些較為明確的建議,但是實(shí)際去調(diào)節(jié)的時(shí)候,還是挺難的,但原則上說(shuō),是可以通過(guò)調(diào)節(jié)這兩個(gè)Flag來(lái)使得收斂問(wèn)題得以解決的,只是得有耐心。 5、kmesh, SIGMA 收斂問(wèn)題還跟kmesh及SIGMA(當(dāng)使用ISMEAR不等于-5 和-4時(shí))的設(shè)置有關(guān)。要達(dá)到同樣的精度,較小的SIGMA則需要較大的kmesh;而且,當(dāng)SIGMA較小時(shí),若kpoints不夠多,也會(huì)出現(xiàn)難收斂的情況。 P.S. 對(duì)于不同系統(tǒng)的計(jì)算,問(wèn)題的原因不一定一樣,因而可能解決之一問(wèn)題的方法也不一定會(huì)一樣。其實(shí)以上大部分都來(lái)自VASP的說(shuō)明書(shū),只是我在遇到收斂問(wèn)題時(shí)試過(guò)這些方法. |

榮譽(yù)版主 (知名作家)
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金蟲(chóng) (著名寫(xiě)手)
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