A Simple Tutorials for calculating Phonon

Calculating Phonon may be simple compared to other calculating process.

More details coule be got at Click🔗 Here

Now I show a simple example for calculting Phonon based on VASP.5.4.4+Phonopy.2.3.2.

Installation and Configuration

It is easy and you can refer this article.click🔗 HERE.

Structural optimisation

It is worth noting that the calculation of the phonon spectrum needs to be fully optimised with high precision for the original cell structure, otherwise false frequencies can easily occur.

I show a example which contain INCAR file

INCAR

SYSTEM = 2D_InSe
ISTART = 0
NWRITE = 2   
PREC   = Accurate
ENCUT  = 500
GGA    = PE
NSW    = 200
ISIF   = 3
ISYM   = 2
NBLOCK = 1   
KBLOCK = 1
IBRION = 2
NELM   = 80     
EDIFF  = 1E-08   
EDIFFG = -0.001 # Perhaps such high accuracy cannot be converged in one step, at which point if an error is reported, try distribution optimisation to make it converge
ALGO   = Normal
LDIAG  = .TRUE.
LREAL  = .FALSE.
ISMEAR = 0       
SIGMA  = 0.02
ICHARG = 2
LPLANE = .TRUE.
#NPAR  = 4   # If you are not using supercomputers, do not add this parameter as it may cause an error to be reported！      
LSCALU = .FALSE.
NSIM   = 4
LWAVE  = .FALSE.
LCHARG = .FALSE.
ICORELEVEL =  1

OPTCELL

For 2d materials,we often add this.Like follwing:

100
110
000

Establishing a supercell with Phonopy code

Rename

Rename Output file（CONTCAR） of the previous step to POSCAR

>cp CONTCAR POSCAR

Establishing a supercell

>phonopy -d --dim="a a 1" 

Rename

>cp POSCAR POSCAR-unitcell
>cp SPOSCAR POSCAR

Calculating Hessian matrix for phonon frequencies

INCAR

ISTART = 0
NWRITE = 2
IBRION = 8    
IALGO  = 38
NELM   = 200
EDIFF  = 1E-07
EDIFFG = -0.001
ISMEAR = 0   
SIGMA  = 0.02
ENCUT  = 500
PREC   = Accurate
LREAL  = .FALSE.
LWAVE  = .FALSE.
LCHARG = .FALSE.
ADDGRID = .TRUE.

KPOINTS

If your machines or Servers'RAM is totally enough,try to increase KPOINTS may be a better choice!

Running tips

It is a wise Initiative to estimate the consume RAM and decrease Number of cores properly.

When entering the operation step of the mechanics matrix, the memory will suddenly increase and this may crash your program. So please allow sufficient running memory when entering the second step.

Data processing

Phonopy will generate FORCE_CONSTRAINS which is based on vasprun.xml.

Generate FORCE_CONSTRAINS

>phonopy --fc vasprun.xml

Self-editing file:band.conf

You should generate by yourself and modify it.

>touch band.conf
>vi band.conf

ATOM_NAME = 
DIM = a a 1 
BAND = 0.5 0.0 0.0  0.0 0.0 0.0  0.333333 0.333333 0.0  0.5 0.0 0.0 
BAND_LABELS = M G K M
FORCE_CONSTANTS = READ

>ENTER->"ESC" and :wq!

Pay attention to "DIM = a a 1"!It depends on "phonopy -d --dim="a a 1"

Generate band.yaml

>phonopy --dim="a a 1" -c POSCAR-unitcell band.conf

And the last process is:

>phonopy-bandplot  --gnuplot> PBAND.dat

Then you will get PBAND.dat and you can draw figures by Origin Gnuplot Matlab etc.(The Phonopy‘s default is 51 Points between two high symmetry points)

More details could be seen at Click🔗 HERE

If the false frequencies still exists,change the "phonopy -d --dim="a a 1"".Whether to take the larger or the smaller often depends on experience！

Sometimes it is unstable in the non-magnetic state, so we need to verify and illustrate the phonon spectrum in the ferromagnetic and antiferromagnetic cases！Don't forget to add the parameter RWIGS and MAGMOM!

For 2D materials,if you use VASP+Phonopy for calculation,It may have littte false frequencies.It is not a great problem,you can show it in your paper!

The simple tutorial is ending and thanks for Yong He !

You can refer to his tutorials!Click🔗 HERE.