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杂化密度泛函之AEXX参数及在此基础上进行GW计算

已有 16681 次阅读 2014-9-8 00:29 |个人分类:电子结构计算|系统分类:科研笔记

关注：

1）杂化密度泛函

2） HSE作为GW方法的输入？

问题

1) 计算自旋轨道耦合作用通常应该设置哪些参数，你有计算自旋轨道耦合作用的输入脚本文件吗？

2) wannier90.win文件中num_wann，num_bands， exclude_bands，及Projections等参数的物理含义是什么？如何确定选值？

3) GW计算中NBANDS，ENCUT、ENCUTGW等参数如何设置？我所采用的脚本是否有误？

4) 你开展过HSE的相关计算吗？有参考脚本吗？

5) 如前所述，采用HSE、GW处理过后，仍未产生带隙，或许应考虑加入自旋轨道耦合作用；请问如何将自旋轨道耦合参数加入到GW或HSE计算输入文件中。

Thanks to Prof. Hong Jiang

你的问题，我现在也说不好。之前我曾经计算过ScN，也是用LDA给出金属态，但采用基于LDA+U的GW可以给出比较准确的带隙。

但是对你 ScH3，由于HSE仍然给出金属态，所以我也不确定用基于LDA+U的GW就足够了。

我觉得一个可以尝试的做法是，增大HSE06中 AEXX参数的值，我相信AEXX足够大时一定会得到一个带隙。

然后再在基础上做GW计算【怎么将HSE结果作为基础，】。

这里的问题是如何确定AEXX，我觉得一种可能性是选择AEXX使得HSE06给出的带隙与基于HSE06得到的GW带隙结果一致。

这是文献里用的一种方法来处理分子体系，对于固体是否适用，也不好说。

Thanks to Huayung

Dear xiaoqiu,

I checked this system with some simple calculations.

The single shot GW method, GW0, indeed cannot give a band gap.

But self-consistent GW, in which the orbitals in G and W are also updated,

predicts a band gap about 1.2 eV (pleasesee the attached figure).

This value is still 0.5 eV smaller than theexperimental 1.7 eV, but can be considered as good at current theoreticallevel.

The discrepancy, in my opinion, might be due to the residual self-interaction introduced in mean-field theory, which cannot be removed completely with GW approxiamtion only (though much better results can beachieved).

To improve the result further, we can consider to employ better DFTorbitals, for example using DFT+U or hybrid functional orbitals instead of the pure LDA/GGA orbitals to feed in GW calculations.

Xiaoqiu, you can check the calculation using the attached scripts by performing a GW0 first and then followed by a self-consistent GW, scGW.

If everythingis OK then you can proceed to the next step, using DFT+U or M06-HF hybridfunctional to produce self-interaction corrected orbitals.

Using these orbitals to initialize the GW calculation, I think we can obtain the correct band gap.

Sincerely YOURS

Geng

从你的结果看HSE杂化泛函对能隙附近的能带结构基本没什么效果，GW有些影响但没能产生带隙，其中的原因并不显而易见。

由于ScH3属于电荷转移绝缘体，在理想的情况下H上应该有两个1s电子，而Sc上剩满壳层的[Ar]核。目前看起来没能产生带隙的原因有可能是电荷转移不完全导致，你可以检查一下费米能级附近的电子是不是还属于Sc。如果Sc上还残余有d电子，你可以用DFT+U的方法劈裂能隙。

由于ScH3中没有高角动量的电子，自旋-轨道耦合我猜测帮助可能不会很大。

要进行自旋-轨道耦合计算，你需要在INCAR中设置LNONCOLLINEAR = T （可能需要重新编译VASP）和 LSORBIT = T，并且去除对称性ISYM = 0。其余的设置与标准的DFT计算没有什么不同。

wannier只是用来分析结果的，其参数不影响具体的计算，GW参数的设置没看出不妥。

究其最终原因，我感觉问题的根源在于电子的自相互作用而非电子间的关联，HSE和GW都不能完全去除电子自相互作用，你可能需要考虑包含100% Hartree-Fock交换能量泛函的方法（例如M06-HF杂化泛函），或者其它Self InteractionCorrection方法。

Sincerely YOURS

Geng

摘自手册：

Amount of exact/DFT exchange and correlation: AEXX, AGGAX, AGGAC and ALDAC tags

AEXX = [real] (fraction of exact exchange) ALDAC= [real] (fraction of LDA correlation energy) AGGAX= [real] (fraction of gradient correction to exchange) AGGAC= [real] (fraction of gradient correction to correlation)

Default:
AEXX	=0.25	for LHFCALC=.TRUE.
	=0.0	for LHFCALC=.FALSE.
AGGAX	=1.0-AEXX
AGGAC	=1.0
ALDAC	=1.0

Specifies the amount of exact exchange and various other exchange and correlation settings. The sum of the fraction of the exact exchange and LDA exchange is always 1.0, and it is not possible to set the amount of LDA exchange independently.

Examples: if AEXX=0.25, 1/4 of the exact exchange is used, and 3/4 of the LDA exchange is added.

For AEXX=0.5, half of the exact exchange is used, and one half of the LDA exchange is added.

The amount of gradient correction to the exchange and the correlation contributions can be set independently, however (some popular hybrid functionals for instance use only 0.8 of the gradient contribition to the exchange).

The GGA flags AGGAX and AGGAC are only used if GGA is already selected (for LDA type calculations no gradient correction will be added regardless of the values supplied for AGGAX and AGGAC).

Note: The defaults are chosen such that the hybrid PBE0 functional is selected for PBE pseudopotentials (the PBE0 functional contains 25 % of the exact exchange, and 75 % of the PBE exchange, and 100 % of the PBE correlation energy).

The resulting expression for the exchange-correlation energy then takes the following simple form:

$.displaystyle E_{.mathrm{xc}}^{.mathrm{PBE0}}=.frac{1}{4} E_{.mathrm{x}} + .frac{3}{4} E_{.mathrm{x}}^{.mathrm{PBE}} + E_{.mathrm{c}}^{.mathrm{PBE}}$

(6.64)

Other sensible values are of course AEXX=1.0 (full Hartree-Fock type calculations).

In this case, VASP also automatically selects ALDAC=0.0 and AGGAC=0.0, to avoid the addition of a (semi-local) correlation energy.

A comprehensive evaluation of the performance of the PBE0 functional, as compared to PBE, can be found in Ref. [92].

摘录：

http://emuch.net/html/201112/3986091.html

首先给出官网的论坛
http://cms.mpi.univie.ac.at/vasp-forum/forum.php
1．计算光学性质(liliangfang) （由于本人非物理与材料出身，一些理论知识欠缺，有错误的地方还请大家批评指正）
可以计算光学性质的第一原理软件很多，比如CASTEP可以直接计算处理处一些光学性质，而vasp可以计算出的是介电函数矩阵，通过介电函数矩阵处理得到光学性质。
关于介电函数，一般的固体物理里面都有定义，如固体物理导论的14.1.1，其第15章是介绍光学性质的。附件1里面附上两片介绍光学性质的文献。
VASP4.6还没有光学模块，所以计算起来比较麻烦，后处理还需小程序。首选4.6需要用PGI（optics这个小程序是基于pgi的）编译，以为后面计算方便，然后还要编译optics这个小程序，是处理计算出来的文件OPTIC，这个文件时用来存放介电函数矩阵的，由于其不能直接打开处理，所以要借助optics。这个程序是Dr. Jürgen Furthmüller写的，可以在他的主页下载（这里找不到主页了，后面找到补上，程序见附件2），如果编译过程遇到问题，可以先在本论坛查找解决方法，也可以给Dr. Jürgen Furthmüller发信咨询（juergen.furthmueller@uni-jena.de）。
至于4.6计算光学性质的步骤，有虫友发过，见附件3VASP5.2已经有光学性质的模块了，计算后再OUTCAR的最近会得到介电函数矩阵，第一部分是介电函数的虚部，第二部分为介电函数实部。得到介电函数的虚部和实部之后，据可以依据公式的推导，得到如折射率与介电函数虚部，实部的关系：

其他一些关系性质与介电函数关系的公式在附件1里面有，如果需要详细推导过程，请查阅相关关系性质计算的文献。
下面以Si为例（个人经验，在这里是为引出更好的计算方法），简单说一下计算过程及参数设（ http://emuch.net/bbs/viewthread.php?tid=2592318 ）。利用杂化泛函（在第2部分由WDD880227做介绍）。
http://emuch.net/bbs/viewthread.php?tid=3753879
计算光学性质的过程中，准确计算能带尤为重要，其直接影响光学性质的计算准确度，附件4里面介绍DFT和HSE06计算出的能带及光学性质的比较。
关于计算结果的讨论，一般计算光学性质的文献都有，如附件5是讨论Si和Ge的。
以上是个人的计算的一下经验，贴出来和大家一起交流学习，有错误之处还请大家指教。另外个人有两个问题，这里提出来希望大家多多指教：
（1）光学性质与能带的关系
（2）光学性质与纳米晶粒尺寸的（定量）关系
2. 杂化泛函计算 (WDD880227)
这里给出论坛里已有的讨论
http://emuch.net/bbs/viewthread.php?tid=3387913&page=1
先给出两篇文献（见2楼）
(1)PHYSICAL REVIEW B 80, 115205 (2009)
(2) PHYSICAL REVIEW B 80, 155124 (2009)
(3) PHYSICAL REVIEW B 80, 205113 (2009)
VASP :HSE Calculation
杂化泛函: 考虑the non-local Fock exchange energy
第一步是结构优化，就是每个原子能量最低.
第二步是静态自洽计算得到电子波函数，这两部和LDA是一样的
第三步就是用上一步的电子波函数做混合泛函计算，主要是第三步混合泛函第（这一步要把ISMEAR改成-5，ISMEAR改成-5电子占据数不会出现负值，对半导体不会出现能级展宽，师姐传授的经验）
第四步是计算能带。杂化泛函的计算时候用的K点和第二步不一样，是用高对称点产生的K点（不用高对称K点也可以，但是计算得到的能带就是和gw一样，是布里渊区的K点）首先把IBZKPT拷贝到KPOINTS里，然后加上高对称点的kpoints，但是高对称点后面要加一个权重因子0 （高对称点的权重因子为0的解释：高对称点就是单独一个点），cat IBZKPT kpoints > KPOINTS, 注意新得到的KPOINTS的K点总数的和是该KPOINTS第二行的数值，这样才能算能带，不过提取的时候用一个特殊的band——plot ，就是截取后面高对称点的值才能得到能带
KPOINTS一般用Monkhorst自动产生，尽量避开用G，六角的时候用G
最新的5.2.12 需要把ENCUTFOCK这个参数换成 PRECFOCK才能计算
杂化泛函是普通泛函所用时间的800-1000倍
杂化泛函参数设置：
LHFCALC = .TRUE.
HFSCREEN = 0.2 (To conform with the HSE06 functional you need to select (HFSCREEN=0.2))
ALGO = Damped
TIME = 0.4
ENCUTFOCK = 0
AEXX =？（AEXX = (fraction of exact exchange)， Other sensible values are of course AEXX=1.0 (full Hartree-Fock type calculations)）
LHFCALC- specifies, whether Hartree-Fock type calculations are performed. At the moment, it is recommended to select an all bands simultaneous algorithm, i.e. ALGO=Damped (IALGO=53) or ALGO=All (IALGO=58) in the INCAR file.
In most cases, it is recommended to use the damped algorithm with suitably chosen timestep. The following setup for the electronic optimization works reliably in most cases:
LHFCALC = .TRUE. ; ALGO = Damped ; TIME = 0.4
If convergence is not obtained, it is recommended to reduce the timestep TIME.
HFSCREEN= determines the range separation parameter in range separated hybrid functionals. In combination with PBE potentials, attributing a value to HFSCREEN will switch from the PBE0 functional (in case LHFCALC=.TRUE.) to the closely related HSE03 or HSE06 functional .
The HSE03 and HSE06 functional replaces the slowly decaying long-ranged part of the Fock exchange, by the corresponding density functional counterpart. The resulting expression for the exchange-correlation energy is given by:

As can be seen above, the separation of the electron-electron interaction into a short- and long-ranged part, labeled SR and LR respectively, is realized only in the exchange interactions. Electronic correlation is represented by the corresponding part of the PBE density functional.
The decomposition of the Coulomb kernel is obtained using the following construction (μ=HFSCREEN):

where
, and µ is the parameter that defines the range-separation, and is related to a characteristic distance, (2/μ), at which the short-range interactions become negligible.
Note: It has been shown that the optimum µ, controlling the range separation is approximately 0.2-0.3 A . To conform with the HSE06 functional you need to select (HFSCREEN=0.2)
It is easily seen from
.
that the long-range term becomes zero for μ=0, and the short-range contribution then equals the full Coulomb operator, whereas for μ= ∞it is the other way around. Consequently, the two limiting cases of the HSE03/HSE06 functional are a true PBE0 functional for μ=0 , and a pure PBE calculation for μ= ∞.

Note: A comprehensive study of the performance of the HSE03/HSE06 functional compared to the PBE and PBE0 functionals can be found in Ref.
The flag ENCUTFOCK is no longer supported in vasp.5.2.4 and newer versions. Please use PRECFOCK instead，ENCUTFOCK=0对应于PRECFOCK=F, 个人经验ENCUTFOCK=0速度比PRECFOCK=F快将近3倍.
我最近主要是用杂化泛函做一步静态自洽计算，用的是普通的KPOINTS，没有用高对称的K点，杂化参数设置就同上面给出的一样。注意杂化泛函计算（不管是自洽计算还是结构优化）之前一定要有一步PBE的自洽计算。

摘录自：

http://blog.sciencenet.cn/blog-417402-764855.html

HSE hybrid functional：Hartree-Fock (HF) type and hybrid functional calculations

Available only in VASP.5.X.

http://cms.mpi.univie.ac.at/vasp/vasp/Hartree_Fock_HF_type_hybrid_functional_calculations.html

INCAR FOR HSE

# output options

LWAVE = .FALSE. # write or don't write WAVECAR

LCHARG = .FALSE. # write or don't write CHG and CHGCAR

LELF = .FALSE. # write ELF

# ionic relaxation

NSW = 100 # number of ionic steps

IBRION = 1 # 2=conjucate gradient, 1=Newton like

ISIF = 3 # 3=relax everything, 2=relax ions only, 4=keep volume fixed

# precision parameters

EDIFF = 1E-7 # 1E-3 very low precision for pre-relaxation, use 1E-5 next

EDIFFG = -1E-3 # usually: 10 * EDIFF

PREC = high # precision low, med, high, accurate

# electronic relaxation

ISMEAR = 0 # -5 = tetraedon, 1..N = Methfessel

SIGMA = 0.1

ENCUT = 600 # cutoff energy

PSTRESS = 0

#ISYM=0

# Choose DFT functional - HSE06

ISTART = 1

LHFCALC = .TRUE. ; HFSCREEN = 0.2

NBANDS = 16

ALGO = All ; TIME = 0.4

PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations

#NKRED = 2 ! omit flag for high quality calculations

http://blog.sciencenet.cn/blog-417402-764855.html

HSE hybrid functional：Hartree-Fock (HF) type and hybrid functional calculations

Available only in VASP.5.X.

http://cms.mpi.univie.ac.at/vasp/vasp/Hartree_Fock_HF_type_hybrid_functional_calculations.html

Subsections

(1) Typical hybrid functional and Hartree-Fock calculations

It is strongly recommended to perform standard DFT calculations first, and to start Hartree-Fock type calculations from a preconverged WAVECAR file.

(a) A typical INCAR file for a Hartree-Fock or hybrid HF/DFT calculation for an insulator or semiconductor has the following input lines:

ISTART = 1

LHFCALC = .TRUE. ;

HFSCREEN = 0.2

NBANDS = number of occupied bands

ALGO = All ;

TIME = 0.4

PRECFOCK = Fast #! used PRECFOCK = Normal for high quality calculations

NKRED = 2 #! omit flag for high quality calculationsFor

(b) For metals and small gap semiconductors it is recommended to use.

ISTART = 1

LHFCALC = .TRUE. ;

HFSCREEN = 0.2

ALGO = Damped ;

TIME = 0.4

PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations

NKRED = 2 ! omit flag for high quality calculations

These input files select the HSE06 functional, which tends to yield very similar thermochemistry as the PBE0 functional, but converges more rapidly with respect to the number of k-points [99]. We thus recommend to apply and use this functional instead of the more demanding PBE0 functional.

The NKRED flag is applicable, if and only if the number of k-points is dividable by NKRED (see Sec. 6.71.9).

PRECFOCK= fast selects a smaller FFT grid for the fast-Fourier-transforms (see Sec. 6.71.5).

For high accuracy NKRED and in particular PRECFOCK= fast should be ommited, but we recommend to do this only after preconverging the orbitals and atomic positions with the flags specified above.

Mind, that the parameter TIME defaults to 0.4, and for the present algorithm this hardly ever needs to be changed.

If divergence is observed, simply decrease TIME until the damped or conjugate gradient algorithm become stable (see Sec. 6.47 and 6.51).

Standard Hartree-Fock type calculations require one to set the flag AEXX = 1.0 to switch on full non-local exchange (local exchange and correlation are automatically switched off):

ISTART = 1 LHFCALC = .TRUE. ; AEXX = 1.0 ; NBANDS = number of occupied bands ALGO = All ; TIME = 0.4 PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations NKRED = 2 ! omit flag for high quality calculations

Concerning NKRED and PRECFOCK the same considerations as above apply. Matter of fact, it is also possible to try to converge using the ``metallic'' setup given above.

(2)Notes

（1）LHFCALC-tag

LHFCALC= .TRUE. | .FALSE.

Default: LHFCALC=.FALSE.

The flag specifies, whether Hartree-Fock type calculations are performed.

At the moment, it is recommended to select an all bands simultaneous algorithm, i.e. ALGO=Damped (IALGO=53) or ALGO=All (IALGO=58) in the INCAR file (see Sec. 6.46 6.47).

The blocked Davidson algorithm ALGO=Normal is, with certain caveat, also supported, whereas calculations for the other algorithms (ALGO=Fast) are not currently supported (note: no warning is printed).

The blocked Davidson algorithm ALGO=Normal is generally rather slow, and in many cases the Pulay mixer will be unable to determine the proper ground-state.

We hence recommend to select the blocked Davidson algorithm only in combination with straight mixing or a Kerker like mixing. The following combination have been successfully applied for small and medium sized systems

LHFCALC = .TRUE. ; ALGO = Normal ; IMIX = 1 ; AMIX = aDecrease the parameter a until convergence is reached.

In most cases, however, it is recommended to use the damped algorithm with suitably chosen timestep. The following setup for the electronic optimization works reliably in most cases:

LHFCALC = .TRUE. ; ALGO = Damped ; TIME = 0.4If convergence is not obtained, it is recommended to reduce the timestep TIME.

（2）HFSCREEN

HFSCREEN determines the range separation parameter in range separated hybrid functionals. In combination with PBE potentials, attributing a value to HFSCREEN will switch from the PBE0 functional (in case LHFCALC=.TRUE.) to the closely related HSE03 or HSE06 functional [93,94,95].

Note: A comprehensive study of the performance of the HSE03/HSE06 functional compared to the PBE and PBE0 functionals can be found in Ref. [99]. The B3LYP functional was investigated in Ref. [100]. Further applications of hybrid functionals to selected materials can be found in the following references: Ceria (Ref. [101]), lead chalcogenides (Ref. [102]), CO adsorption on metals (Refs. [103,104]), defects in ZnO (Ref. [105]), excitonic properties (Ref. [106]), SrTiO and BaTiO (Ref. [107]).

LTHOMAS= .TRUE. | .FALSE.

Default: LTHOMAS=.FALSE.

If the flag LTHOMAS is set, a similar decomposition of the exchange functional into a long range and a short range part is used. This time, it is more convenient to write the decomposition in reciprocal space:

$.displaystyle .frac{4 .pi e^2}{.vert{.bf G}.vert^2}=S_{.mu}(.vert{.bf G}.vert)+... ...{.vert{.bf G}.vert^2} -.frac{4 .pi e^2}{.vert{.bf G}.vert^2 +k_{TF}^2} .right),$

(6.69)

where $k_{TF}$ is the Thomas-Fermi screening length. HFSCREEN is used to specify the parameter $k_{TF}$ . For typical semi-conductors, the Thomas-Fermi screening length is about 1.8 Å $^{-1}$ , and setting HFSCREEN to this value yields reasonable band gaps for most materials.

In principle, however, the Thomas-Fermi screening length depends on the valence electron density; VASP determines this parameter from the number of valence electrons (POTCAR) and the volume and writes the corresponding value to the OUTCAR file:

Thomas-Fermi vector in A = 2.00000Since, VASP counts the semi-core states and -states as valence electrons, although these states do not contribute to the screening, the values reported by VASP are, however, often incorrect. Details can be found in literature [96,97,98]. Another important detail concerns that implementation of the density functional part in the screened exchange case. Literature suggests that a global enhancement factor (see Equ. (3.15) in Ref. [98]) should be used, whereas VASP implements a local density dependent enhancement factor $z= k_{TF}/.bar k$ , where is the Fermi wave vector corresponding to the local density (and not the average density as suggested in Ref. [98]). The VASP implementation is in the spirit of the local density approximation.

（3） ALGO

Default
ALGO	=	Normal

The ALGO tag is a convenient option to specify the electronic minimisation algorithm in VASP.4.5 and later versions. Except for ``None'' and ``Nothing'', ``Exact'' and ``Diag'' (which must be spelled out), the first letter determines the applied algorithm. Conjugate, Subrot, Eigenval, Exact, None and Nothing are only supported by VASP.5.2.12 and newer versions.

ALGO = Normal selects IALGO = 38 (blocked Davidson iteration scheme), whereas ALGO = Very_Fast selects IALGO = 48 (RMM-DIIS). A faily robust mixture of both algorithm is selected for ALGO = Fast. In this case, Davidson (IALGO = 38) is used for the initial phase, and then VASP switches to RMM-DIIS (IALGO = 48). Subsequencly, for each ionic update, one IALGO = 38 sweep is performed for each ionic step (except the first one).

The ``all band simultaneous update of orbitals'' can be selected using ALGO = Conjugate or ALGO = All (IALGO = 58, in both cases the same conjugate gradient algorithm is used). A damped velocity friction algorithm is selected using ALGO = Damped (IALGO = 53). ALGO = Subrot selects subspace rotation or diagonalization in the sub-space spanned by the calculated NBANDS orbitals (IALGO = 4). ALGO = Exact or ALGO = Diag performs an exact diagonalization (IALGO = 90), and we recommend to use this if more than 30-50 % of the states are calculated (e.g. for or RPA calculations). ALGO = Eigenval allows to recalculate one electron energies, density of state and perform selected postprocessing using the current orbitals (IALGO = 3) e.g. read from WAVECAR. ALGO = None or ALGO = Nothing allows to recalculate the density of states (eigenvalues from WAVECAR, e.g. using different smearing or tetrahedron method) or perform other selected postprocessing using the current orbitals and one electron energies (IALGO = 2) e.g. read from WAVECAR.

（4）PRECFOCK

PRECFOCK: FFT grid in the Hartree-Fock and GW related routines

PRECFOCK= Low | Medium | Fast | Normal | Accurate

Default: PRECFOCK=Normal

The PRECFOCK parameter controls the FFT grid for the exact exchange (Hartree-Fock) routines, i.e. it is possible to chose a different grid for the exact exchange part, and for the local Hartree and DFT potentials. In fact, the exchange is rather insensitive to the FFT grids, and in many cases a rather coarse grid can be used to calculate the overlap density and the potentials. Since the exact exchange requires the evaluation of an overlap density (compare 6.59)

$.displaystyle .phi_{{.bf k}n}^{*}({.bf r}).phi_{{.bf q}m}^{*}({.bf r})$

errors in the convolution (aliasing errors) are only avoided, if the FFT grid contains all Fourier components up to twice the plane wave with the largest wave vector ( $2 .vert G_{.rm cut}.vert$ ).

For Low and Fast, however, the smallest possible FFT grid, which just encloses the cutoff sphere ( $.vert G_{.rm cut}.vert$ ) determined by the plane wave cutoff (ENCUT), is used. This accelerates the calculations by roughly a factor two to three, but causes slight changes in the total energies and some noise in the calculated forces. The corresponding FFT grid that is used in the Hartree Fock routines is written to the OUTCAR file after the lines

FFT grid for exact exchange (Hartree Fock)For PRECFOCK=Normal, the FFT grid for the exact exchange is identical to the FFT grid used for the orbitals for PREC=Normal in the DFT part. For PRECFOCK=Accurate, the FFT grid for the exact exchange is identical to the FFT grid used for the orbitals for PREC=Accurate in the DFT part (any combination of PREC and PRECFOCK is allowed).

For PRECFOCK=Fast, Normal and Accurate, the augmentation charges--which are required to restore the norm and dipoles of the overlap density on the plane wave grid --are made soft, such that an accurate presentation on the plane wave grid is possible even for relatively coarse FFT grids. The sphere size is printed out after

Radii for the augmentation spheres in the non-local exchangeThe following table summarises the possible setting:

PRECFOCK	FFT grid	augmentation charge	advantage/disatvantage
VASP.5.2.2 compatible, not recommended
Low	$G_{.rm cut}^a$	identical to standard DFT	large noise in forces/energy errors
Medium	identical to std. FFT	identical to standard DFT	some noise in forces/good energy
VASP.5.2.4 and newer, recommended
Fast	$G_{.rm cut}^a$	very soft augmentation charge	some noise in forces/good energy
Normal	3/2 $G_{.rm cut}^a$	soft augmentation charge	accurate forces and energy
Accurate	2 $G_{.rm cut}^a$	soft augmentation charge	very accurate forces and energy

$^a .quad .frac{ .hbar^2}{2 m_e} .vert G_{.rm cut}.vert^2 = {.tt ENCUT}$

soft augmentation charge: radius for augmentation sphere is increased by factor 1.25 compared to default

very soft augmentation charge: radius is increased by factor 1.35 compared to default except for

like charge, for the

channel the radius of the augmentation sphere is increased by a factor 1.25

Even PRECFOCK=Fast yields fairly low noise in the forces and virtually no egg-box effects (aliasing errors). In the forces, the noise is usually below 0.01 eV/Å. For PRECFOCK=N and PRECFOCK=A, noise is usually not an issue, and the accuracy is sufficient even for phonon calculations in large supercells.

摘录自：

http://vaspleee.lofter.com/post/2cceb3_e5aaf5

不少虫友（包括我自己）都是新接触杂化泛函计算，都希望对此有深入的了解，因此，专门开设该贴供大家一起交流讨论、共同学习进步。
1.首先给出两个链接
（1）vasp论坛关于HSE的链接
http://cms.mpi.univie.ac.at/vasp-forum/search.php
（2）vasp官网杂化泛函部分
http://cms.mpi.univie.ac.at/vasp/vasp/Hartree_Fock_HF_type_hybrid_functional_calculations.html
2.给出本版里关于杂化泛函计算的帖子链接
(1)此前同版主liliangfang一起开的杂化泛函计算的帖子链接
http://emuch.net/bbs/viewthread.php?tid=3986091
(2)版主uuv2010的交流讨论帖
http://emuch.net/bbs/viewthread.php?tid=3387913&page=1
(3)版主liliangfang的资源帖
http://emuch.net/bbs/viewthread.php?tid=3753879
(4)密度泛函的发展及应用贴
http://emuch.net/bbs/viewthread.php?tid=1695674
3.注意HSE计算的K点设置
版主liliangfang计算光学性质时为保证介电谱收敛要加密K点，他的帖子中有提到。
HSE计算能带时，要用到高对称K点。

举报删除此信息

uuv2010 (站内联系TA)

请教两个问题：
1.对于杂化泛函的计算可以用少一些的k点，那么这个k点的数目是按照收敛性测试的方式得到？还是有其他比较可靠的经验的取法？
2.如何提高计算速度？增大并行核数能有效提高计算速度吗？或者使用更大内存能提高计算速度？
谢谢！

WDD880227 (站内联系TA)

2楼: Originally posted by uuv2010 at 2012-01-06 13:21:48:
请教两个问题：
1.对于杂化泛函的计算可以用少一些的k点，那么这个k点的数目是按照收敛性测试的方式得到？还是有其他比较可靠的经验的取法？
2.如何提高计算速度？增大并行核数能有效提高计算速度吗？或者使用 ...

1.杂化泛函的K点也是以收敛性为基础，也有一些经验参照，在计算能带的时候就可以根据MS中给出的K path来确定高对称的K点。
2.提高计算速度可以设置ENCUTFOCK=0,这个参数设置比PRECFOCK=F速度快很多。当然了，适当增大并行的核数以及使用大内存都能够提高计算速度，不过VASP的并行速率不是随并行核数增大先行增大的，而是有一个最高点吧。:hand:

chuanghua304 (站内联系TA)

这个帖子很好，跟楼主们学到不少东西！下面是我的一点体会！
http://cms.mpi.univie.ac.at/vasp ... topic.php?4.6633.20 这个帖子大家一定看哈，很权威啊！下面是Georg Kresse给我的回信。
Dear professor:
> I am a VASP user. I want to calculate band structure and optical property with HSE06.I have read the post about "Band Structure Calculation With HSE06" in VASP forum.But now I also have several question about "admin's answer".http://cms.mpi.univie.ac.at/vasp ... topic.php?4.6633.10
> Now my questions are as follows:
> 1.Dose "-1) First perform " for HSE scf need the WAVECAR of DFT calculation? In this step,how to set the parameter ICHARG?
Doing DFT calculations first is always a good idea for HSE.
ICHARG does not matter when you start a HSE calculation (it is disregarded).
> 2. The "-5) Perform a second VASP run: " is A Hartee-Fock calculation ? Dose this step for band need the WAVECAR and CHGCAR file of prevous HSE06 calculation ? How to set the
> parameters ISTARTand ICHARG?
>
WAVECAR only. CHGCAR is not relevant for restart of HSE calculations.
Georg Kresse
--
Univ.-Prof. Dr. Georg Kresse email: Georg.Kresse@univie.ac.at
Computational Materials Physics voice: +43-1-4277-51411
Univ. Wien, Sensengasse 8/12 fax: +43-1-4277-9514 (or 9513)
A-1090 Wien, AUSTRIA cmp.mpi.univie.ac.at cms.mpi.univie.ac.at/kresse

liliangfang (站内联系TA)

4楼: Originally posted by chuanghua304 at 2012-01-14 10:34:08:
这个帖子很好，跟楼主们学到不少东西！下面是我的一点体会！
http://cms.mpi.univie.ac.at/vasp ... topic.php?4.6633.20 这个帖子大家一定看哈，很权威啊！下面是Georg Kresse给我的回信。
Dear p ...

首先说这位虫友讲的好，官网当然比较权威啦，呵呵，其实有可能你没认真看说明书，这些在说明书里面都有说明的，所以说当我们使用某种软件或者方法的时候要先看他的说明，看懂了再解决问题，这样学习能快一点

jghe (站内联系TA)

3楼: Originally posted by WDD880227 at 2012-01-06 14:59:14:
1.杂化泛函的K点也是以收敛性为基础，也有一些经验参照，在计算能带的时候就可以根据MS中给出的K path来确定高对称的K点。
2.提高计算速度可以设置ENCUTFOCK=0,这个参数设置比PRECFOCK=F速度快很多。当然了，适 ...

The flag ENCUTFOCK is no longer supported in vasp.5.2.4 and newer versions. Please use PRECFOCK instead (see Sec. 6.69.5).
http://cms.mpi.univie.ac.at/vasp/vasp/ENCUTFOCK_FFT_grid_in_Hartree_Fock_related_routines.html

whw19850730 (站内联系TA)

我最近再用杂化泛函HSE计算材料性质的时候遇到了一些问题，向您请教一下，我用HSE计算磁性钙钛矿 CaMnO3 SrMnO3 晶格常数计算的很准确，但是计算CaTcO3的材料与别人用HSE计算差很远（PHYSICAL REVIEW B 83, 220402(R) (2011)），我想可以调节计算的应该是AEXX = 0.25 和HFSCREEN = 0.2这两个参数吧，我一般都用默认值，但是不知道具体怎么调节，我感觉HFSCREEN参数对于金属体系应该设的小一些，对于绝缘的可以设定的大一些吧？AEXX如果对于默认的参数计算晶格常数偏大就应该设的小一些，对于默认的参数计算晶格常数偏小就调节的大一些，（在计算CaTcO3文章里，他们用的AEXX =0.1，但是我用0.1严重偏小，用默认的0.25又偏大）不知道我理解的对不对，所以向你请教一下设定参数经验，还有我发现ENCUTFOCK = 0 ，NKRED = 2，这两个参数必须得开启，说明书说对高精度可以忽略，但我忽略了发现慢了很多倍，我感觉不如大K点去提高精度快。

WDD880227 (站内联系TA)

7楼: Originally posted by whw19850730 at 2012-03-07 01:02:02:
我最近再用杂化泛函HSE计算材料性质的时候遇到了一些问题，向您请教一下，我用HSE计算磁性钙钛矿 CaMnO3 SrMnO3 晶格常数计算的很准确，但是计算CaTcO3的材料与别人用HSE计算差很远（PHYSICAL REVIEW B 83, 22040 ...

我用HSE计算的是ZnO，HFSCREEN = 0.2，而AEXX = 0.36是根据文献取的，计算的结果也跟文献报道一致，一般经验参数都需要自己测试，你可以用小体系在0.1和0.25之间取值测试，以后对于这个体系就可以用测试出的合适的值。ENCUTFOCK = 0 可以很大程度上提高计算速度，而NKRED 我一直取的是默认值，没有注意到你说的这个问题。

enola (站内联系TA)

chuanghua304 ,你好
http://cms.mpi.univie.ac.at/vasp ... topic.php?4.6633.20
帖子打不开，可以告诉我帖子名吗？我去搜下，谢谢，一并你的总结

WDD880227 (站内联系TA)

9楼: Originally posted by enola at 2012-05-25 11:33:08
chuanghua304 ,你好
http://cms.mpi.univie.ac.at/vasp ... topic.php?4.6633.20
帖子打不开，可以告诉我帖子名吗？我去搜下，谢谢，一并你的总结

你去vasp 论坛上搜一下就有~~~O(∩_∩)O~

chuanghua304 (站内联系TA)

去注册哈VASP forum http://cms.mpi.univie.ac.at/vasp-forum/ 搜索band structure for HSE06

ya_mde (站内联系TA)

7楼: Originally posted by whw19850730 at 2012-03-07 01:02:02
我最近再用杂化泛函HSE计算材料性质的时候遇到了一些问题，向您请教一下，我用HSE计算磁性钙钛矿 CaMnO3 SrMnO3 晶格常数计算的很准确，但是计算CaTcO3的材料与别人用HSE计算差很远（PHYSICAL REVIEW B 83, 220402( ...

你好我想问一下你用HSE算磁性的步骤是什么另外怎样加磁性谢谢啦新手求救:cry:

99098585 (站内联系TA)

本人利用杂化泛函计算失败原因如何如下，如何处理？谢谢！
LDA part: xc-table for Pade appr. of Perdew
POSCAR, INCAR and KPOINTS ok, starting setup
WARNING: small aliasing (wrap around) errors must be expected
FFT: planning ...( 1 )
WAVECAR not read
entering main loop
N E dE d eps ncg rms rms(c)
rank 14 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 14: killed by signal 9
rank 12 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 12: killed by signal 9
rank 35 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 35: killed by signal 9
rank 29 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 29: killed by signal 9
rank 28 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 28: killed by signal 9
rank 27 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 27: killed by signal 9
rank 26 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 26: killed by signal 9
rank 25 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 25: killed by signal 11
rank 24 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 24: killed by signal 11
rank 47 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 47: killed by signal 11
rank 46 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 46: killed by signal 9
rank 45 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 45: killed by signal 9
rank 38 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 38: killed by signal 9
rank 37 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 37: killed by signal 9
rank 36 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 36: killed by signal 11
rank 11 in job 1 node1_56151 caused collective abort of all ranks
exit status of rank 11: killed by signal 9