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.

Perfect and displaced supercells were created by

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

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 displaed supercell forces by

% phono3py --cf3 disp-{00001..01254}/vasprun.xml --cfz disp-00000/vasprun.xml

In the example directory, FORCES_FC3 is compressed to FORCES_FC3.lzma.
After unzipping FORCES_FC3.lzma, to obtain fc3.hdf5 and normal fc2.hdf5,

% phono3py --sym-fc

Using 13x13x9 sampling mesh, lattice thermal conductivity is calculated by

% phono3py --mesh="13 13 9" --fc3 --fc2 --br

kappa-m13139.hdf5 is written as the result. The lattice thermal
conductivity is calculated as k_xx=228.2 and k_zz=224.1 W/m-K at 300 K.

With --nac option, non-analytical term correction is applied reading
the Born effective charges and dielectric constant from BORN file:

% phono3py --mesh="13 13 9" --fc3 --fc2 --br --nac

This changes thermal conductivity at 300 K to k_xx=235.7 and
k_zz=219.1. The shape of phonon band structure is important to
fullfill energy and momentum conservations.

Use of larger supercell of 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

To create force constants, FORCES_FC2 is needed.

% phono3py --cf2 disp-{00001..00006}/vasprun.xml --cfz disp-00000/vasprun.xml

Then re-create force constants and calculate thermal conductivity,

% phono3py --sym-fc
% phono3py --mesh="13 13 9" --fc3 --fc2 --br --nac

k_xx=236.0 and k_zz=222.2 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.