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（LDA）仅仅是相关部分表示方法不同，所有现代应用的局域密度泛函都基于Ceperly和Alder`s在８０年代对均匀电子气总能量的Monte Carlo模拟。

广义梯度近似（ＧＧＡ）：ＧＧＡ是Jacob阶梯的第二个台阶，将电子密度的梯度也作为一个独立的变量（|?n(r)|），在描述交换－相关能方面，梯度引入了非定域性。ＧＧＡ泛函包含了两个主要的方向：一个称为“无参数”，泛函中新的参数通过已知形式中参数或在其它准确理论帮助下得到。另外一个就是经验方法，未知参数来自于对实验数据的拟和或通过对原子和分子性质准确的计算。Perdew,Burke and Emzerhof(PBE)以及Perdew-Wang from 1991(PW91)是无参数的，在量子化学中广泛采用的GGA，比如Becke,Lee,Parr and Yang(BLYP)是经验性。LYP校正采用了密度的二阶Laplace算符，因此严格上讲属于Jacob阶梯的第三阶，但通常仍然归类为GGA. （见后面英文介绍）

请问： 在用CASTEP计算材料空位缺陷时，如何才能实现只取一个空位呢 *在build下的symtrey有make P1 *不是降低对称性，是构建超胞

make supper cell

然后就可以删去一个原子了

正常的话如果晶体是原胞，直接删除一个原子可能造成很大影响

可以建大一点的超晶胞(比如2×2×2超晶胞)然后删掉一个原子，这样比较合理， 毕竟缺陷浓度是很低的。

*都可以啊！先看一下show symmetry 是P1就可以直接删一个，如果不是就换成P1，一般 make supercell 后自动变成P1了，你可以根据自己所需的浓度选择其中一种方式

MS无法收敛

请大家帮忙看看了,掺杂Eu的体系,一开始提示增加empty band,减小smear,都做了,把精度设置到coarse,可最后还是在100轮后提示无法收敛.

------------------------------------------------------------------------ <-- SCF

*Warning* max. SCF cycles performed but system has not reached the groundstate.

Current total energy, E = -10141.84970726 eV Current free energy (E-TS) = -10141.84970726 eV (energies not corrected for finite basis set)

NB est. 0K energy (E-0.5TS) = -10141.84970726 eV

******************************************************** Warning: electronic minimisation did not converge during finite basis set correction.

******************************************************** Checkpoint file cannot be written.

Error calculate_finite_basis : Convergence failed when doing finite basis set correction. Error calculate_finite_basis : Convergence failed when doing finite basis set correction.

******************************************************** Warning: electronic minimisation did not converge during finite basis set correction.

******************************************************** Checkpoint file cannot be written.

[1] MPI Abort by user Aborting program ! [1] Aborting program!

[0] MPI Abort by user Aborting program ! [0] Aborting program!

回答：1.增加smearing 容易收敛，但是太大可能结果会有些问题。 2.增加循环的圈数， 3.增加空带数目，

4.体系有自旋单电子的，要设置自旋极化，如果设置非自旋极化，可能不收敛 5. 如果是金属体系，比较难收敛，可以试试修改k点和empty band 试试看。

1. 几何优化可以在多大范围内改变原子的位置啊？感觉每次优化后的位置调整不是很多

啊？

2. 大家在算能带和态密度的时候的时候是用单点能计算给出能带还是几何优化给出能带

啊？

回答：问题1

几何优化的目的是寻找压力最小的几何结构，原子位置改变不多是因为你建的构形比较合理，比如直接从软件数据库中导入的结构在0压力下改变很小，如果加个压力就会变化大一些。 问题2

一般都是优化的时候算，如果你想算特定构形的能带或其它性质，就可以用单点能；

【表面模拟】castep计算中遇到的几个问题

PW91 Perdew-Wang generalized-gradient approximation Perdew and Wang (1992) BP Becke exchange plus Perdew correlation Becke (1988), Perdew and Wang (1992) PBE Perdew-Burke-Ernzerhof correlation Perdew et al. (1996)

RPBE Revised PBE functional by Hammer et al. Hammer et al. (1999)

HCTH Hamprecht, Cohen, Tozer and Handy functional Boese and Handy (2001)

BLYP Becke exchange plus Lee-Yang-Parr correlation Becke (1988), Lee et al. (1988) BOP Becke One Parameter functional Tsuneda et al. (1999)

VWN-BP BP functional with the local correlation replaced by the VWN functional. Vosko et al. (1980), Becke (1988), Perdew and Wang (1992)

VWN: The Vosko-Wilk-Nusair (VWN) functional is the most popular LSD correlation potential. It uses a fit to accurate numerical results (by Ceperly and Alder) of a uniform electron gas. Ceperley and Alder performed quantum Monte Carlo calculations on a uniform electron gas at low and high spin limits for several electron densities. VWN uses the Pade interpolation procedure to fit the CA results for both the para and ferro states and for low and high densities. DMol3 uses the best VWN (so called \

PWC: The Perdew-Wang (PWC) functional is a recent parameterization of the Ceperley and Alder data, which corrects some VWN problems with fitting. PWC is the default functional for DMol3 calculations.

The local spin-density (LSD) approximation accurately predicts structures, vibrations, and relative energies of covalent systems; however, bond energies are seriously overestimated. The local DFT should not be used for systems with weak bonds, such as hydrogen bonds. These problems with the LSD method can be corrected to a large extent by using the so-called gradient-corrected (or nonlocal) functionals.

P91, BP, BLYP, BOP: DMol3 supports several nonlocal exchange and correlation functionals. The most popular, the Becke exchange functional (B88) is used in conjunction with the Perdew-Wang correlation functional (BP) or the Lee-Yang-Parr correlation functional (BLYP). The so-called generalized gradient corrected (GGA) functional, by Perdew and Wang (P91) was derived by considering low and high density regimes and by enforcing various summation rules.

PBE: The PBE (Perdew, Burke and Enzerhof) functional (1996, 1997) is another GGA functional in which all the parameters (other then those in its LDA component) are fundamental constants. The exchange part of this functional is similar to the Becke formula (1986), and the correlation part is close to the Perdew-Wang functional (1986).This functional has a strong physical background, reliable numerical performance and it is frequently used in DFT calculations.

RPBE: More recently, Hammer, Hansen and Norskov (1999) proposed a modified version of the PBE formula that improves considerably thermochemical results. So far this functional, called RPBE, has been mainly used for solids.

HCTH: The HCTH functional, named for the authors' initials (Hamprecht et al., 1998), represents a \philosophy in designing a DFT functional. Assuming that the exact functional will never be found, they propose a flexible form of gradient corrected functional that is fitted to the training set of molecules. The default for the current implementation, the so called HCTH/407 functional, that was obtained by fitting to the set of the 407 atomic and molecular systems (Boese and Handy, 2001). This functional was found to predict a much improved thermochemistry for inorganic and hydrogen bonded systems. The standalone keyword for this functional is hcth407. The original HCTH-type functionals can be activated by keyword hcth93 (Hamprecht et al, 1998) and hcth147 (Boese et al. 2000).

Although the NLSD methods are significantly better than the LSD method, particularly in studying chemical reactions, the NLSD methods may still lead to reaction barriers that are too low.

VWN-BP: The VWN-BP functional is recommended for COSMO and COSMO-RS studies.

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1、问：用MS构造晶体时要先确立空间群,可是那些空间群的代码是啥意思啊,看不懂,我想做的是聚乙烯醇的晶体,嘿嘿,也不知道去哪 可以查到它的空间群

答：A、要做晶体，首先要查询晶体数据，然后利用晶体数据再建立模型。晶体数据来源主要是文献，或者一些数据库，比如CCDC。

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