约束随机相近似（CRPA）U值测试

关于CRPA方法的官网教程，可以看VASP-wiki：

CRPA of SrVO3 – Vaspwiki

这里我写一个简明的总结。

第一步：进行传统的DFT计算

我们以SrVO3为例，将文件夹命名为1，准备INCAR文件如下：

System  = SrVO3                        # system name         
NBANDS = 36                            # small number  of bands  
ISMEAR = 0                             # Gaussian smearing  
EDIFF = 1E-8                           # high precision for groundstate calculation
KPAR = 2                               # parallelization of k-points in two groups 

POSCAR如下：

SrVO3 # PBE 3rd order fit  (6x6x6 k-points)
3.84652
 +1.0000000000  +0.0000000000  +0.0000000000 
 +0.0000000000  +1.0000000000  +0.0000000000 
 +0.0000000000  +0.0000000000  +1.0000000000 
Sr V O
 1 1 3
Direct
 +0.0000000000  +0.0000000000  +0.0000000000 
 +0.5000000000  +0.5000000000  +0.5000000000 
 +0.5000000000  +0.5000000000  +0.0000000000 
 +0.5000000000  +0.0000000000  +0.5000000000 
 +0.0000000000  +0.5000000000  +0.5000000000

KPOINTS：

Automatically generated mesh
 0
Gamma
 4 4 4
 0 0 0

准备好POTCAR之后，提交VASP任务进行计算。第一步运行成功后，我们会获得包含WAVECAR的波函数。

第二步：获取DFT计算的虚拟轨道及长波极限

建一个新的文件夹命名为2，将第一步计算的文件全部复制进去，修改INCAR，增加以下参数：
NBANDS = 96                         
ALGO = Exact
NELM = 1
LOPTICS = .TRUE.
修改后的完整INCAR如下：

System  = SrVO3                        # system name         
  
ISMEAR = 0                             # Gaussian smearing  
EDIFF = 1E-8                           # high precision for groundstate calculation
KPAR = 2                               # parallelization of k-points in two groups  

NBANDS = 96                         
ALGO = Exact
NELM = 1
LOPTICS = .TRUE.

提交VASP，这时会产生新的WAVECAR和CHGCAR

第三步：CRPA计算

将第二步的文件夹内容全部复制到一个新的文件夹，命名为3

准备wannier90.win文件，如下：

num_wann =    3
num_bands=   96

# PBE energy window of t2g states (band 21-23)
dis_win_min = 6.4
dis_win_max = 9.0

begin projections
 V:dxy;dxz;dyz
end projections

修改INCAR，增加以下参数：
NCSHMEM = 1
ALGO = CRPA
PRECFOCK = Fast
NTARGET_STATES = 1 2 3
LWRITE_WANPROJ = .TRUE.
修改后完整的INCAR如下：

System  = SrVO3                        # system name         
  
ISMEAR = 0                             # Gaussian smearing  
EDIFF = 1E-8                           # high precision for groundstate calculation
KPAR = 2                               # parallelization of k-points in two groups  

NBANDS = 96                         

NELM = 1
LOPTICS = .TRUE.

NCSHMEM = 1
ALGO = CRPA
PRECFOCK = Fast
NTARGET_STATES = 1 2 3
LWRITE_WANPROJ = .TRUE.

最后提交任务计算