这篇博客是我学习声子谱计算的一些笔记,因为通常在判断一个体系是否具有稳定性的时候,需要计算其声子谱,最近也在慢慢摸索第一性计算的相关工具和知识,就一起整理出来.

Phonopy 安装

VASP的安装这里就不多说了,可以参考VASP编译安装这篇博客中的内容,这里主要先整理如何安装Phonopy, 完全参考的是官网上的教程,从官网上的安装教程来看,最好是先安装好Ananconda,关于Ananconda的安装可以参考做数值计算好用的软件及杂项整理这篇博客中的内容.在安装好了Ananconda之后,开始安装Phonopy

conda install -c conda-forge phonopy

我是在Linux服务器上安装的,所以在安装Ananconda与Phonopy时都是以root用户进行的,中间只会简单的进行库函数的更新与Phonopy的安装,过程耗时非常少,耐心等待几分钟即可.

自洽

首先在计算声子谱的时候,要先保证完成了结构优化,因为我对结构优化还不是很熟悉,所以我在这里整理的只是如何正确的完整声子谱计算的整个流程,我是利用一个已知的结构,在自洽计算的结果上进行声子谱计算的.

下面是我做自洽计算的VASP输入文件

INCAR

Global Parameters
ISTART =  1            (Read existing wavefunction; if there)
ISPIN =  2           (Spin polarised DFT)
ICHARG =  2         (Non-self-consistent: GGA/LDA band structures)
LREAL  = .FALSE.       (Projection operators: automatic)
ENCUT  =  400        (Cut-off energy for plane wave basis set, in eV)
PREC   =  Normal       (Precision level)
LWAVE  = .TRUE.        (Write WAVECAR or not)
LCHARG = .TRUE.        (Write CHGCAR or not)
ADDGRID= .TRUE.        (Increase grid; helps GGA convergence)

# GGA = PE

#  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)

#  NPAR   = 4           (Max is no. nodes; don't set for hybrids)

#  NWRITE = 2           (Medium-level output)

#  KPAR   = 2           (Divides k-grid into separate groups)

#  NGX    = 500         (FFT grid mesh density for nice charge/potential plots)

#  NGY    = 500         (FFT grid mesh density for nice charge/potential plots)

#  NGZ    = 500         (FFT grid mesh density for nice charge/potential plots)
 
Static Calculation
ISMEAR =  0            (gaussian smearing method)
SIGMA  =  0.05         (please check the width of the smearing)
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)
NBANDS = 64

# NBANDS = 128
LSORBIT    = .TRUE.    (Activate SOC)

POSCAR

Bi2Se3
1.0
-2.069  -3.583614  0.000000
 2.069  -3.583614  0.000000
 0.000   2.389075  9.546667
Bi   Se
 2   3
Direct
 0.3990    0.3990    0.6970
 0.6010    0.6010    0.3030
 0     0     0.5
 0.2060    0.2060    0.1180
 0.7940    0.7940    0.8820             

KPOINTS
```
Monkhorst Pack
0
G
 12  12  3
 0   0   0
```
完整自洽计算之后,下一步就开始构建超胞计算声子谱
```
phonopy -d --dim="4 4 1"
```
这里进行扩胞的时候,要让3个方向都大于$10A$的量级,运行这个命令之后会生成很多个POSCAR-001之类的文件,不过我们使用的暂时只有SPOSCAR这个文件