phono3py/example/AlN-LDA

This is the example of the wurtzite-type AlN phono3py calculation. The VASP code was used with 500 eV and LDA as XC functional. The experimental lattice parameters were used and the internal positions of atoms were relaxed by calculation. The 3x3x2 and 5x5x3 supercells were chosen for fc3 and fc2. The 6x6x4, 2x2x2, 1x1x2 k-point sampling meshes with Gamma-centre in the basal plane and off-Gamma-centre along c-axis were employed for the unit cell, fc3 supercell, and fc2 supercell, respectively. For the DFPT calculation of Born effective charges and dielectric constant, the 12x12x8 k-point sampling mesh with the similar shift was used.

Then the forces were calculated with the above settings. FORCES_FC3 and FORCES_FC2 were created with subtracting residual forces of perfect supercell from all displaced supercell forces.

Perfect and displaced supercells were created by

% phono3py --dim 3 3 2 -c POSCAR-unitcell -d

In the example directory, FORCES_FC3 is compressed to FORCES_FC3.xz. After unzipping FORCES_FC3.xz (e.g., using xz -d), to obtain fc3.hdf5 and fc2.hdf5 using symfc (the results without using symfc, i.e., finite difference method, are shown at the bottom of this README)

% phono3py-load --symfc -v

Lattice thermal conductivity is calculated by

% phono3py-load --mesh 40 --br --ts 300

kappa-m15158.hdf5 is written as the result. Parameters for non-analytical term correction (NAC) is automatically read from those stored in phono3py_disp.yaml or BORN file. The lattice thermal conductivity is calculated as k_xx=242.8 and k_zz=226.5 W/m-K at 300 K. Without NAC, k_xx=233.6 and k_zz=222.2.

Use of larger supercell for fc2 may change the shape of phonon band structure. To see it, first regenerate phono3py_disp.yaml with --dim-fc2 option,

% phono3py --dim 3 3 2 --dim-fc2 5 5 3 -c POSCAR-unitcell -d

Then re-create force constants and calculate thermal conductivity,

% phono3py-load --symfc -v
% phono3py-load --br --mesh=40 --ts 300

If phono3py_disp.yaml is renamed to phono3py_disp_dimfc2.yaml, it can be specified at the first argument of phono3py-load command:

% phono3py-load phono3py_disp_dimfc2.yaml --symfc -v
% phono3py-load phono3py_disp_dimfc2.yaml --br --mesh=40 --ts 300

k_xx=240.2 and k_zz=230.1 are obtained. In the case of this example, we can see that the larger fc2 supercell contributes little, which means that the 3x3x2 supercell was good enough to obtain a good shape of phonon band structure.

Using the finite difference method implemented in phono3py, lattice thermal conductivities are obtained as k_xx=251.2 and k_zz=233,4 without using the large fc2 supercell and k_xx=249.4 k_zz=236.9 using the large fc2 supercell.