vasp计算新手，计算步骤参考的是vasp官网教程：
不正确的地方希望大家批评指正，另外我还有很多理论知识要补，希望能和大家一起学习、交流、进步~
以CaO的频率依赖介电函数和光学性质计算为例：
之一步，静态自洽计算，以得到WAVECAR
在完成结构优化后，复制其CONTCAR, POTCAR到静态计算的文件夹2scf; 并复制提交计算的脚本vasp.slurm到2scfcp CONTCAR POTCAR ../2scf
cp vasp.slurm ../2scf
进入2scf文件夹，并将CONTCAR复制为POSCAR cd ../2cf
cp CONTCAR POSCAR
使用vaspkit生成KPOINTS，使用Gamma方法，间距设置为0.02（光学性质计算需要采用比较密的k点），KPOINTS文件如下 K-Spacing Value to Generate K-Mesh: 0.020
0
Gamma
18 18 18
0.0 0.0 0.0
使用vaspkit生成INCAR, 并修改，如下Global Parameters
SYSTEM = CaO SCF
ISTART = 1 (Read existing wavefunction, if there)
ISPIN = 2 (Spin polarised DFT)
MAGMOM = 2*0.6
# ICHARG = 11 (Non-self-consistent: GGA/LDA band structures)
LREAL = .FALSE. (Projection operators: automatic)
ENCUT = 520 (Cut-off energy for plane wave basis set, in eV)
# PREC = Accurate (Precision level: Normal or Accurate, set Accurate when perform structure lattice relaxation calculation)
LWAVE = .TRUE. (Write WAVECAR or not)
LCHARG = .TRUE. (Write CHGCAR or not)
ADDGRID= .TRUE. (Increase grid, helps GGA convergence)
# LVTOT = .TRUE. (Write total electrostatic potential into LOCPOT or not)
# LVHAR = .TRUE. (Write ionic + Hartree electrostatic potential into LOCPOT or not)
# NELECT = (No. of electrons: charged cells, be careful)
# LPLANE = .TRUE. (Real space distribution, supercells)
# NWRITE = 2 (Medium-level output)
# KPAR = 2 (Divides k-grid into separate groups)
# NGXF = 300 (FFT grid mesh density for nice charge/potential plots)
# NGYF = 300 (FFT grid mesh density for nice charge/potential plots)
# NGZF = 300 (FFT grid mesh density for nice charge/potential plots)
Static Calculation
I *** EAR = 0 (gaussian *** earing method)
SIGMA = 0.01 (please check the width of the *** earing)
LORBIT = 11 (PAW radii for projected DOS)
NEDOS = 2001 (DOSCAR points)
NELM = 60 (Max electronic SCF steps)
EDIFF = 1E-08 (SCF energy convergence, in eV)
其中，改动就是增加了SYSTEM,ISPIN=2,MAGMOM,ENCUT=520,SIGMA=0.01。注意LWAVE = .TRUE.,这样才能生成下一步要用的WAVECAR文件
检查INCAR,POSCAR,POTCAR,KPOINTS,vasp.slurm都在，提交作业 *** atch vasp.slurm
等待计算结束，耗时177s第二步，基于独立粒子近似（Independent-Partical Approximation）的频率依赖介电函数和光学性质计算
参考的是vasp官网手册上对SiC的频率依赖介电函数的计算 - 在2scf文件夹中的OUTCAR文件查看NBANDS的值，后续的NBANDS设置为该值的2~3倍
grep NBANDS OUTCAR
新建ipa-optical文件夹，将2scf文件夹里的WAVECAR KPOINTS POTCAR POSCAR vasp.slurm复制到ipa-optical文件夹中。mkdir ../ipa-optical
cp WAVECAR KPOINTS POTCAR POSCAR vasp.slurm ../ipa-optical
使用vaspkit生成INCAR文件，在命令行依次输入vaspkit-1-101-OP,得到INCAR和INCAR.step2.lef。其中之一个来自vasp官网手册SiC的频率依赖介电函数的计算上The independent-particle picture小节，是基于独立粒子假设的；第二个考虑了局域场效应，来自Including local field effects小节。必须要在之一个计算的基础上（且INCAR中LPEAD=.TRUE.）,才能进行第二个计算。本小节进行之一个计算，简称IPA。INCAR修改如下,增加了ISPIN MAGMOM ENCUT,修改NBANDS=96,CSHIFT=0.15(该值越大，曲线越光滑),LPEAD=.TRUE.(生成WAVEDER文件)Optical properties
ALGO = Exact
NBANDS = 96 (Set this parameters manually)
LOPTICS = .TRUE.
CSHIFT = 0.150
NEDOS = 2000
I *** EAR = 0
SIGMA = 0.01
EDIFF = 1.E-8
LPEAD = .TRUE. (Write the derivative of the cell-periodic part of the orbitals)
ISPIN = 2
MAGMOM = 2*0.6
ENCUT = 520
检查INCAR,WAVECAR,POSCAR,POTCAR,KPOINTS,vasp.slurm都在，提交作业 *** atch vasp.slurm
等待计算结束，耗时367s 。使用官网脚本由gnuplot绘制的介电函数图 使用vaspkit 711命令，得到光学系数，如EXTINCTION.dat ABSORPTION.dat等。使用origin画图，对比CSHIFT=0.15和0.1的结果。可知0.15时曲线更加光滑。第三步，考虑局域场效应的频率依赖介电函数和光学性质计算
复制ipa-oiptical文件夹为rpa-opticalcp ipa-optical rpa-optical -r
进入rpa-optical文件夹,修改INCAR参数 cp INCAR.step.lef INCAR
INCAR 如下
# Frequency dependent dielectric tensor with and
# without local field effects in RPA
# N.B.: beware one first has to have done a
# calculation with ALGO=Exact, LOPTICS=.TRUE.
# and a reasonable number of virtual states (see above)
# be sure to take the same number of bands as for
# the LOPTICS=.TRUE. calculation, otherwise the
# WAVEDER file is not read correctly
ALGO = CHI
NBANDS = 96 (Take the same number of bands in the previous step)
I *** EAR = 0
SIGMA = 0.01
EDIFF = 1.E-8
LWAVE = .FALSE.
LCHARG = .FALSE.
# LRPA = .FALSE. (Set .FALAE. to include contributions from DFT exchange and correlation)
ENCUT = 520
ISPIN = 2
MAGMOM = 2*0.6
检查INCAR,WAVECAR,POSCAR,POTCAR,KPOINTS,vasp.slurm都在，提交作业 *** atch vasp.slurm
等待计算结束，耗时很久 使用vaspkit 711命令，得到光学系数，如EXTINCTION.dat ABSORPTION.dat等。
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