Force constants IO¶

Hiphive provides read and write functionality for force constants in a few different formats. Currently the following formats are supported.

GPUMD¶

We also support functionality for writing force constants and other relevant files to GPUMD format. GPUMD is a packages that allows one to calculate for example thermal conductivities using molecular dynamics (MD) simulations both via the Green-Kubo and the homogenenous non-equilibrium MD approach.

Conversion betweeen ShengBTE and phono3py¶

The following snippet demonstrates the conversion from phono3py to ShengBTE:

from hiphive import ForceConstants
from ase.io import read

prim = read('POSCAR')
supercell = read('SPOSCAR')
fcs = ForceConstants.read_phono3py(supercell, 'fc3.hdf5')
fcs.write_to_shengBTE('FORCECONSTANTS_3rd', prim)

Conversion in the opposite direction is achieved as follows:

from hiphive import ForceConstants
from ase.io import read

prim = read('POSCAR')
supercell = read('SPOSCAR')
fcs = ForceConstants.read_shengBTE(supercell, 'FORCECONSTANTS_3rd', prim)
fcs.write_to_phono3py('fc3.hdf5')

This allows one for example to check the equivalence of the thermal conductivity calculated using either one of the two codes. This is demonstrated for the case of a monolayer of MoS2 in the following example. The original force constants were generated using the thirdorder.py code associated with ShengBTE. Only phonon-phonon scattering was considered as a lifetime limiting process (i.e. neither isotope nor boundary scattering were included). Calculations were carried out within the relaxation time approximation (RTA) for both codes. In the case of ShengBTE we also solved the Boltzmann transport equation self-consistently (sc).

../_images/kappa_MoS2_shengBTE_phono3py.svg — Thermal conductivity of a monolayer of MoS2 using both phono3py and ShengBTE.¶