# VASP & phono3py calculation¶

## Workflow¶

Create POSCARs with displacements

This is the same way as usual phonopy:

% phono3py -d --dim="2 2 2" -c POSCAR-unitcell

`disp_fc3.yaml`

and`POSCAR-xxxxx`

files are created.If you want to use larger supercell size for second-order force constants (fc2) calculation than that for third-order force constants (fc3) calculation:

% phono3py -d --dim_fc2="4 4 4" --dim="2 2 2" -c POSCAR-unitcell

In this case,

`disp_fc2.yaml`

and`POSCAR_FC2-xxxxx`

files are also created.Run VASP for supercell force calculations

To calculate forces on atoms in supercells,

`POSCAR-xxxxx`

(and`POSCAR_FC2-xxxxx`

if they exist) are used as VASP (or any force calculator) calculations.It is supposed that each force calculation is executed under the directory named

`disp-xxxxx`

(and`disp_fc2-xxxxx`

), where`xxxxx`

is sequential number.Collect

`vasprun.xml`

’sWhen VASP is used as the force calculator, force sets to calculate fc3 and fc2 are created as follows.

% phono3py --cf3 disp-{00001..00755}/vasprun.xml

where 0755 is an example of the index of the last displacement supercell. To perform this collection,

`disp_fc3.yaml`

created at step 1 is required. Then`FORCES_FC3`

is created.When you use larger supercell for fc2 calculation:

% phono3py --cf2 disp_fc2-{00001..00002}/vasprun.xml

`disp_fc2.yaml`

is necessary in this case and`FORCES_FC2`

is created.Create fc2.hdf and fc3.hdf

% phono3py --dim="2 2 2" -c POSCAR-unitcell

`fc2.hdf5`

and`fc3.hdf5`

are created from`FORCES_FC3`

and`disp_fc3.yaml`

. This step is not mandatory, but you can avoid calculating fc2 and fc3 at every run time.When you use larger supercell for fc2 calculation:

% phono3py --dim_fc2="4 4 4" --dim="2 2 2" -c POSCAR-unitcell

Similarly

`fc2.hdf5`

and`fc3.hdf5`

are created from`FORCES_FC3`

,`FORCES_FC2`

,`disp_fc3.yaml`

, and`disp_fc2.yaml`

.Thermal conductivity calculation

An example of thermal conductivity calculation is:

% phono3py --fc3 --fc2 --dim="2 2 2" --mesh="11 11 11" \ -c POSCAR-unitcell --br

or with larger supercell for fc2:

% phono3py --fc3 --fc2 --dim_fc2="4 4 4" --dim="2 2 2" --mesh="11 11 11" \ -c POSCAR-unitcell --br

This calculation may take very long time.

`--thm`

invokes a tetrahedron method for Brillouin zone integration for phonon lifetime calculation, which is the default option. Instead,`--sigma`

option can be used with the smearing widths.In this command, phonon lifetimes at many grid points are calculated in series. The phonon lifetime calculation at each grid point can be separately calculated since they are independent and no communication is necessary at the computation. The procedure is as follows:

First run the same command with the addition option of

`--wgp`

:% phono3py --fc3 --fc2 --dim="2 2 2" --mesh="11 11 11" \ -c POSCAR-unitcell --br --wgp

`ir_grid_points.yaml`

is obtained. In this file, irreducible q-points are shown. Then distribute calculations of phonon lifetimes on grid points with`--write_gamma`

option by:% phono3py --fc3 --fc2 --dim="2 2 2" --mesh="11 11 11" \ -c POSCAR-unitcell --br --write_gamma --gp="[grid ponit(s)]"

After finishing all distributed calculations, run with

`--read_gamma`

option:% phono3py --fc3 --fc2 --dim="2 2 2" --mesh="11 11 11" \ -c POSCAR-unitcell --br --read_gamma

Once this calculation runs without problem, separately calculated hdf5 files on grid points are no more necessary and may be deleted.