關注：

1) ?U參數的加入

2) 自旋極化的考慮

3) 鐵磁、反鐵磁的考慮

來自文章的計算方法介紹

The similar MSUs of Pu di- and trihydride provide aframework within which intermediate compositions can be exploredcomputationally.

The calculationspresented here are limited to unit cells with four Pu sites and between eightand twelve H atoms.

Initial unit cells correspond to the two MSUsshown in Fig. 1(a) and in Fig. 1(b) (where the chevron shape is made into anactual unit cell) with added and removed H atoms, respectively.

These initialcon_gurations often relax surprisingly slow with false plateaus, which requirerather small convergence criteria to overcome (see below).

These unitcells limit the current study to structures with AB and ABC stacking. A systematic study of whether the Pu hydrides favor otherstacking sequences will likely shed more light on the system but also require signifficantlymore computational effort.

Thecalculations discussed here neglect thermal effects. Contributions to the free energy from thephonons in particular are important, given the small mass of the H atoms.【氫原子的熱振動對能量影響比較大】

The currentresults doreveal many small energy differences betweenmagnetic states and various conffigurations of the H atoms, which eventhe zero-point energy will affect.

However, in additionto being beyond the scope of this work, the calculation of phonons and including their thermal effectswill not likely overcome the inaccuracy inherent in the density functional theory(DFT) method.

Connectionsmade between the results and experimental data do involve thermal effects inthe form of comparisons with the energy scale set by room temperature, but themain conclusions involve large enough energy differences to be immune to neglectedcontributions from the phonons.【忽略聲子貢獻，可以？】

The resultspresented here originate in DFT calculations using theVASPpackage.17,18

The calculations make use of the generalized gradientapproximation (GGA) of Perdew, Burke, and Ernzerhof.19The Pu(5f6,6d8?,7s2) and H(1s) electrons are treated in the valence withprojector-augmented wave potentials.20

The calculations employ the linear tetrahedron methodwith Blochl corrections,21ak-point mesh of density 60 _A􀀀1, and an energy cuto_ of 500eV.

Theself-consistent cycles are converged to within 10-5meV to enable the 10-4meV ionic stopping criteria needed to overcome the falseplateaus mentioned above. The calculations allow spin polarization and compare twotypes of magnetic structure, ferromagnetic (FM) and antiferromagnetic (AFM).【如何開展此項計算？】

Because DFT inthe GGA fails to describe PuH3as a semiconductor,6the effects of including either strong electroncorrelation and spin-orbit coupling are investigated.

Some results reported here stem from calculations thattreat the on-site Coulomb repulsion between 5felectrons with aHubbard parameterU(GGA+U) in the rotationally invariant form of Dudarevet al.22

In this form the Hubbard parameterUand theexchange parameterJappear only in the differenceU -J, throughoutthis report the difference is simply referred to asU.

A single valueforU(4 eV) for all stoichiometries allows a comparison of thecalculated energies and the evaluation of formation energies.

While Aiet al.suggestspin-orbit coupling (SOC) can be neglected,6the results presented hereshow some energy differences small enough for SOC to matter.

網絡摘錄：

發信人: valenhou (AAA), 信區: Gaussian

標 題: Re: 有人用VASP算過磁性體系嗎？

發信站: BBS 大話西游站 (Tue Jun 3 09:43:22 2003), 轉信

你說的是對的。計算體系的磁性，第一步就是要讓ISPIN=2。如果要進一步考慮具體的

磁序，在設置MAGMON等等參數。

如果只指定了ISPIN=2,而沒有去設置MAGMON，則這種情況是計算體系的鐵磁性，此時

每個原子的MAGMON都相等，默認值為1。

【 在 hsg221 (升仙啦) 的大作中提到: 】

是不是就是說，如果我算一個體系，不是反鐵磁也不是亞鐵磁，就直接

ISPIN=2就可以了，不用管MAGMON？

【 在 valenhou (AAA) 的大作中提到: 】

: 你想哪幾個原子指定有初始磁矩，值可正可負，單位為波爾磁矩ub。

: 一般設置MAGMON是在考慮反鐵磁或亞鐵磁情況下。

網絡摘錄2

SPIN ?= ? ? ?2

MAGMOM = 0 0 4 0 0 4 0 0 4 0 0 4 0 0 4

SAXIS = 0 0 1這是五個原子的磁矩都向z軸的設置 ? 你照著弄下

如何用VASP計算鐵磁、反鐵磁和順磁

順磁，意味進行non-spin polarized的計算，也就是ISPIN=1。

鐵磁，意味進行spin-polarized的計算，ISPIN=2，而且每個磁性原子的初始磁矩設置為一樣的值，也就是磁性原子的MAGMOM設置為一樣的值。

對非磁性原子也可以設置成一樣的非零值(與磁性原子的一樣)或零，最后收斂的結果，非磁性原子的local磁矩很小，快接近0，很小的情況，很可能意味著真的是非磁性原子也會被極化而出現很小的local磁矩。

反鐵磁，也意味著要進行spin-polarized的計算，ISPIN=2，這是需采用反鐵磁的磁胞來進行計算，意味著此時計算所采用的晶胞不再是鐵磁計算時的最小原胞。[超胞？！！！]

比如對鐵晶體的鐵磁狀態，你可以采用bcc的原胞來計算，但是在進行反鐵磁的Fe計算，這是你需要采用sc的結構來計算，計算的晶胞中包括兩個原子，你要設置一個原子的MAGMOM為正的，另一個原子的MAGMOM設置為負，但是它們的絕對值一樣。因此在進行反鐵磁的計算時，應該確定好反鐵磁的磁胞，以及磁序，要判斷哪種磁序和磁胞是最可能的反鐵磁狀態，那只能是先做好各種可能的排列組合，然后分別計算這些可能組合的情況，最后比較它們的總能，總能最低的就是可能的磁序。同樣也可以與它們同鐵磁或順磁的進行比較。了解到該材料究竟是鐵磁的、還是順磁或反鐵磁的。

亞鐵磁，也意味要進行spin-polarized的計算，ISPIN=2，與反鐵磁的計算類似，不同的是原子正負磁矩的絕對值不是樣大。非共線的磁性，那需采用專門的non-collinear的來進行計算，除了要設置ISPIN，MAGMOM的設置還需要指定每個原子在x,y,z方向上的大小。這種情況會復雜一些。

舉個例子來說，對于Mn-Cu(001)c(2x2)這種體系，原胞里面有2個Mn原子，那么你直接讓兩個Mn原子的MAGMOM的絕對值一樣，符號相反就可以了，再加上ISPIN=2。這樣就可以實現進行反鐵磁的計算了。

來自：VASP手冊

MAGMOM= [real array]Default:

MAGMOM=NIONS*1.0 for ISPIN = 2

=3*NIONS*1.0 for non-collinear magnetic systems

Specifies the initial magnetic moment for each atom, if and only if ?ICHARG=2, ?or if the CHGCAR file contains no magnetisation density (ICHARG=1).

If one is searching for a spin polarised (magnetic or antiferromagnetic) solution, ?it is usually safest to start from larger local magnetic moments, because in ?some cases, the default values might not be sufficiently big. A save default is usually the experimental magnetic moment multiplied by 1.2 or 1.5.It is important to emphasize that the MAGMOM tag is ?used only, if the CHGCAR file holds no information on the magnetisation density, and if the initial charge density is not calculated from the orbitals supplied in ?the WAVECAR file.

This means that the MAGMOM tag is useful for two kind of calculationsCalculations starting from scratch with no WAVECAR and CHGCAR file.

Calculations starting from ?a non magnetic WAVECAR and CHGCAR file (ICHARG=1). Often such calculations converge more reliably to the desired magnetic configuration than calculations of the first kind. Hence, if you have problems to converge to a desired magnetic solution, try to calculate first the non magnetic groundstate, and continue from the generated WAVECAR and CHGCAR file. For the continuation job, you need to setISPIN=2

ICHARG=1in the INCAR file.

Starting from VASP.4.4.4, VASP also determines whether the magnetic moments ?supplied in the MAGMOM line break the symmetry. If they do, the corresponding symmetry operations are removed ?and not applied during the symmetrization of charges and forces. This means that antiferromagnetic calculations can be performed by ?specifying anti-parallel magnetic moments for the atoms in the cell MAGMOM = 1 -1

As an example consider AF bcc Cr with the POSCAR file: Cr: AF

2.80000

1.00000 .00000 .00000

.00000 1.00000 .00000

.00000 .00000 1.00000

2

Kartesisch

.00000 .00000 .00000

.50000 .50000 .50000

With the MAGMOM line specified above, VASP should converge to the proper groundstate. In this example, the total net magnetisation ?is matter of factly zero, but it is possible to determine the local magnetic moments by using the RWIGS or LORBIT tags (see sections 6.346.33).

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