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lascqy

银虫 (小有名气)


[交流] HSE能带计算中ISYM参数的问题

在用HSE计算能带的过程中,按照论坛里的K点设置方法,
band structures using hybrid functionals have to be calculated the following way:
-) First perform a selfconsistent Hartree-Fock/HSE calculation using a conventional KPOINTS file.
-) Copy the IBZKPT file to KPOINTS, and explicitely add all desired k-points along high-symmetry lines of the BZ that are needed for the bandstructure plot. Add the points at the end of the KPOINTS file, but set the weights of these added k-points to 0.
-) Do not forget to set the number of k-points in KPOINTS correctly (to the number of the k-points used in the standard mesh PLUS the number of the k-points along the lines), such that all k-points are used for the calculations.
-) NKRED can not be used.
-) Perform a second VASP run:
It is recommended to use the Davidson algorithm, since it converges that eigen energies at the new k-points fastest. Since VASP terminates when the total energy is converged to a certain threshold, it is important to force VASP to do a minimum number of steps, so that the orbitals at the new k-points are fully converged (note: since their weight is zero, they do not contribute to the total energy).
This can be done using e.g.

ALGO = N ; NELMIN = 5 ! Davidson, minimum 5 scf-steps
IBRION = 1 ! Use simple charge mixer, since
Pulay might blow up

-) The KS-eigenvalues of the states along the high-symmetry lines are written in OUTCAR, EIGENVAL, vasprun.xml; please cut the k-points required for the bandstructure from one of these files and proceed as usual (using p4vasp or any other graphics tool you usually use to produce bandstructure-plots)

Note: A Hartee-Fock calculation can NOT be continued from an existing CHGCAR file, since the non-local exchange is not determined by the charge density but by the density matrix and/or the KS-orbitals.

在ISYM=0或者2的时候貌似能带结构有很大区别,但在普通的GGA计算中没有这个现象,不知道这是不是我的个别现象呢,有没有人做过这个的来指点下?
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lascqy

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引用回帖:
2楼: Originally posted by WDD880227 at 2012-03-05 19:28:36:
没有注意到这个问题,我在计算的时候ISYM是默认值,计算出来的能带没有问题

默认值是ISYM=2,也就是有对称性的情况,你有没有把你的结果跟其他本材料的能带对比一下,我计算的结果ISYM=0时能对上,但是ISYM=2时就差别很大了
3楼2012-03-06 11:37:49
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小木虫(金币+0.5):给个红包,谢谢回帖
franch(金币+2): 谢谢回帖交流。。。。 2012-03-05 21:36:17
没有注意到这个问题,我在计算的时候ISYM是默认值,计算出来的能带没有问题
2楼2012-03-05 19:28:36
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ya_mde

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小木虫: 金币+0.5, 给个红包,谢谢回帖
引用回帖:
3楼: Originally posted by lascqy at 2012-03-06 11:37:49
默认值是ISYM=2,也就是有对称性的情况,你有没有把你的结果跟其他本材料的能带对比一下,我计算的结果ISYM=0时能对上,但是ISYM=2时就差别很大了...

难怪我看他们之前用HSE算Si能带的 设了ISYM= 0 但是还不是不知道为什么会造成这种区别 
4楼2012-11-22 14:10:11
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lengqiang

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小木虫: 金币+0.5, 给个红包,谢谢回帖
版主,HSE计算能带时,ISYM需要怎样设置,0 or 2;计算DOS时,ISYM需要怎样设置那,谢谢。还有一个问题,我在用HSE时,加上NPAR=1,就报错,停止运算,有什么解决办法吗,谢谢
5楼2012-11-24 14:21:33
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