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1) 自旋极化、旋轨耦合、加U等哪几项需要同时设置
2)只有先自旋极化了,才可能考虑加U或旋轨耦合?
手册说明:
LDAUTYPE=2 (Default): The simplified (rotationally invariant) approach to the LSDA+U, introduced by Dudarev et al. [91]. This flavour of LSDA+U is of the following form:
LSDA 局域自旋密度近似,当然要设置ISPIN=2了!!
LDAUTYPE=4: Same as LDAUTYPE=1, but LDA+U instead of LSDA+U (i.e. no LSDA exchange splitting). In the LDA+U case the double counting energy is given by,
LDA局域谜底近似,是否意味着可以不设置ISPIN=2,但U和J需单独设置,参考上面的公式
It is important to be aware of the fact that when using the L(S)DA+U, in general the total energy will depend on the parameters and . It is therefore not meaningful to compare the total energies resulting from calculations with different and/or (c.q. in case of Dudarev's approach).
Furthermore, since LDA+U usually results in aspherical charge densities at and atoms we recommend to set LASPH = .TRUE. in the INCAR file for gradient corrected functionals (see Sec. 6.44). For CeO for instance, identical results to the FLAPW methods can be only obtained setting LASPH = .TRUE.
Note on bandstructure calculation: The CHGCAR file also contains only information up to LMAXMIX (defaulted to 2) for the on-site PAW occupancy matrices. When the CHGCAR file is read and kept fixed in the course of the calculations (ICHARG=11), the results will be necessarily not identical to a selfconsistent run. The deviations can be (or actually are) large for L(S)DA+U calculations. For the calculation of band structures within the L(S)DA+U approach, it is hence strictly required to increase LMAXMIX to 4 (d elements) and 6 (f elements). (see Sec. 6.63).
网络摘录:
http://emuch.net/html/201004/2007448.html
作者: nkleof
vasp计算DOS有一种方法,就是以较低k网格达到收敛,再以很高的k网格通过ICHARG=11读取自洽CHGCAR进行DOS计算。
我昨天进行了这样的计算,但是在计算中进行了+U,如下是INCAR
PREC = Accurate
LREAL = A
IALGO = 48
NPAR = 8
NSIM = 8
ISTART = 1
ICHARG = 11
NELMIN = 4
LORBIT = 12
EDIFF = 1E-5
ISMEAR = -5
EMIN = -20
EMAX = 20
NEDOS = 11000
ISPIN = 2
LDAU = .TRUE.
LDAUTYPE = 2
LDAUL = -1 2 -1
LDAUU = 0 2 0
LDAUJ = 0 0 0
LDAUPRINT = 2
其中自洽收敛是以11 11 11网格,非自洽DOS是以21 21 21网格,另外也进行了21 21 21网格的自洽计算进行对比。
如下是三次的DOS 图,分别为k11网格自洽的DOS,在k11网格自洽基础上k21的DOS结果,k21网格自洽的DOS
从图上可以看到,在k11自洽基础上进行k21的ICHARG=11的DOS结果和其他两个有点不同,费米面以上的部分有所变化。
所以,我猜测可能是因为是INCAR里面的+U设置在后来的非自洽计算中重复起了作用,使得实际作用的U值成了4eV。即原来以U=2进行了自洽计算,得到的CHGCAR已经包含2eV 的Coulomb repulsion,后来进行非自洽计算时INCAR中的+U设置又起了作用,再加上了2eV的Coulomb repulsion,所以出来的DOS结果和原来U=2时的不同。【见上面的手册说明?】
希望有高手来证实一下,或者解释一下k21的非自洽结果与原自洽结果的DOS不同的原因。
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U=4的计算结果出来了,证明我前面提到的猜测不正确,U=4的DOS和U=2,ICHARG=11的DOS并不相同。其实从上个帖子的DOS图可以看出来,当U值增大到4时,费米面以上的那部分峰肯定会向着高能量方向移动一段距离,而不是几乎在原地不动。
网络摘录:
http://emuch.net/html/201007/2225276.html
J的值的意义与LDAUTYPE有关的。当LDAUTYPE为2时,U-J的差值才有有意义,即有效的U参数。
至于有效U参数的值怎么选取,通过线性响应的方式来估测,类似pwscf里面的。要么将U值从小测到大,并计算结果同实验结果(比如电子结构等)进行比较,然后选取一个合适的值。再要不然,参考文献中的值。
我看说明书里面说的是:in Dudarev’s approach the parametersU and J do not enter seperately, only the difference (U ¡J) is meaningfull.
并且对于LDAUTYPE,
1 Rotationally invariant LSDA+U according to Liechtenstein et al.
4 Idem 1., but LDA+U instead of LSDA+U (i.e. no LSDA exchange splitting)
2 Dudarev’s approach to LSDA+U (Default)
那是不是说LDAUTYPE=2时只有U-J的值有意义呢?
我还想请问一下:如果我不打开自旋(用GGA+U算)的话,那么可以设置ISPIN的值为1然后将LDAUTYPE能选择为2吗?还是说非自旋计算时只能将LDAUTYPE设置为4呢?
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