||
关注:
1) 虚频的起因;
2) 如何分析虚频由哪些原子朝哪些方向的振动引起的;
3) kpoints 或k-mesh密度如何通过影响自洽计算精度来影响声子的计算
4) 反铁磁或铁磁参数设置后,优化计算通常会改变晶格参数,采用优化后改变了的晶格参数计算声子谱?
5) DFPT计算声子谱可以不扩胞,只需要提高k-mesh密度(如0.03)即可,这比扩胞后, 采用粗网格(k-mesh=0.04或0.05)计算效果还要好。
6) 一些参数设置 NDOWN,
1. INCAR分析:
System=PuH3
PREC=Accurate
GGA=PE
ISMEAR=0
SIGMA=0.05
ENCUT=550
EDIFF=0.1E-5
EDIFFG=-0.01
LREAL=.FALSE.
IBRION=8
IALGO=38
LORBIT=11
LDAU=.TRUE.
LMAXMIX=6
LDAUTYPE=2
LDAUL= -1 3
LDAUJ= 0.0 0.51
LDAUU= 0.0 4.5
LASPH=.TRUE.
ISPIN=2
MAGMOM= 0 0 0 0 0 0 2 2
KSPACING=.251327412287 【数值很奇怪哈!】
2. 参数解释:
(1) KSPACING 无KPOINTS文件情形
Default:
KSPACING = 0.5
KGAMMA = .TRUE.
The tag KSPACING determines the number of k-points if the KPOINTS file is not present (see Sec. 5.5). KSPACING is the smallest allowed spacing between k-points in units of Å. The number of k-points increases when the spacing is decreased. The number of k-points in the direction of the first, second and third reciprocal lattice vector is determined by the equations
(3)LORBIT 计入分波声子密度
LORBIT = .TRUE. | .FALSE. (VASP.3.2)
LORBIT = 0 | 1 | 2 | 5 | 10 | 11 | 12 (VASP.4.X and later)
This flag determines, together with an appropriate RWIGS (see section 6.33), whether the PROCAR or PROOUT files (see section 5.21) are written.
The file PROCAR contains the spd- and site projected wavefunction character of each band. The wavefunction character is calculated, either by projecting the orbitals onto spherical harmonics that are non-zero within spheres of a radius RWIGS around each ion (LORBIT=1, 2), or using a quick projection scheme relying that works only for the PAW method (LORBIT=10,11,12, see below).
If the LORBIT flag is not equal zero, the site and l-projected density of states is also calculated.
If the projector augmented wave method is used, LORBIT can also be set to 10, 11 or 12. This alternative setting selects a quick method for the determination of the spd- and site projected wave function character and does not require the specification of a Wigner-Seitz radius in the INCAR file (the RWIGS line is neglected in this case). The method works only for PAW POTCAR files and not for ultrasoft or norm conserving pseudopotentials
(4)NUPDOWN :强制设置自旋向下电子数为0,则近似认为是AFM设置?
NUPDOWN [integer] (up from VASP.4.X)
Allows calculations for a specific spin multiplet, i.e. the the difference of the number of electrons in the up and down spin component will be kept fixed to the specified value.
There is a word of caution required: If NUPDOWN is set in the INCAR file the initial moment for the charge density should be the same. Otherwise convergence can slow down.
When starting from atomic charge densities (ICHARG=2), VASP will try to do this automatically by setting MAGMOM to NUPDOWN/NIONS. The user can of course overwrite this default by specifying a different MAGMOM (which should still result in the correct total moment).
If one initializes the charge density from the one-electron wavefunctions, the initial moment is always correct, because VASP ``pushes'' the required number of electrons from the down to the up component. Initiallizing the chargedensity from the CHGCAR file (ICHARG=1), however, the initial moment is usually incorrect!
kpoints 或k-mesh密度测试:
The three qualities of k-point separation for CASTEP (1/Angstrom) >>>
coarse.le..08 & medium.le..05 & fine.le..04
Please input the quality of Monkhorst-Pack grid (Default is .035) >>>
0.04
(1)the quality of Monkhorst-Pack grid=0.045
K-Points
0
Monkhorst Pack
3 3 5
0 0 0
447 f/i= 0.002526 THz 0.015872 2PiTHz 0.084261 cm-1 0.010447 meV
448 f/i= 0.005017 THz 0.031522 2PiTHz 0.167345 cm-1 0.020748 meV
449 f/i= 5.995156 THz 37.668674 2PiTHz 199.976860 cm-1 24.793980 meV
450 f/i= 7.474510 THz 46.963733 2PiTHz 249.322818 cm-1 30.912101 meV
(2)the quality of Monkhorst-Pack grid=0.04
K-Points
0
Monkhorst Pack
4 4 6
0 0 0
447 f/i= 0.002744 THz 0.017243 2PiTHz 0.091541 cm-1 0.011350 meV
448 f/i= 0.003664 THz 0.023023 2PiTHz 0.122227 cm-1 0.015154 meV
449 f/i= 4.739132 THz 29.776843 2PiTHz 158.080416 cm-1 19.599481 meV
450 f/i= 7.669601 THz 48.189524 2PiTHz 255.830343 cm-1 31.718931 meV
网络摘录:尊重版权,采用实名制
刘立仁-新师大(275560060) 2013/10/30 4:42:30
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