openmaterials.ai / codes / phono3py

phono3py: phonon lifetimes and thermal conductivity from third-order force constants

A supercell code that fits third-order force constants to DFT forces, computes three-phonon linewidths on symmetry-reduced grids and solves the linearized Boltzmann equation.

What it is and how it works

Linewidths across the Brillouin zone

The imaginary part of the phonon self energy, from the three-phonon interaction strength and the tetrahedron method, is mapped over the zone for nine zincblende compounds among the 33 studied (Togo 2015).

Supercell finite displacements

Single and pair displacements of 0.03 A in supercells, reduced by site symmetry, recovered by crystal symmetry. Forces come from an external code like VASP (Togo 2015).

Symmetry-reduced q grids

Gamma-centred regular grids, point group, time reversal and permutation symmetry cut the q, q' pairs. Lifetimes at irreducible points spread over many nodes (Togo 2023).

Linear tetrahedron method

Energy conservation in the self energy and joint density of states is integrated analytically over 24 tetrahedra per grid point by a module returning weights (Togo 2023).

RTA or direct LBTE solution

Kappa from mode heat capacity, group velocity and lifetime in single-mode RTA, or from the direct solution of the linearized Boltzmann equation, and isotopes (Togo 2015).

Finite temperature displacements

Random supercell displacements drawn from harmonic oscillators at a given temperature, valid when all commensurate modes are stable, for averaged properties (Togo 2023).

What people do with it

  • 33zincblende and wurtzite compounds, RTA and LBTETogo 2015
  • 0.03 Aatomic displacement for second and third orderTogo 2015
  • 7.26e2W/m/K, cubic BN at 300 K with isotopes, LBTETogo 2015

CsPbBr3, particle and wave heat flow

The Wigner conductivity, run in phono3py, gives at 300 K about 1/3 of kappa_xx from populations and 2/3 from coherences, closer to experiment. At 50 K populations give 3/4 (Simoncelli 2022). Simoncelli 2022

Janus MoSSe monolayer

Phono3py with VASP in the RTA gives a room temperature kappa of 13.90 W/m/K for MoSSe, between 23.15 for MoS2 and 11.54 for MoSe2, at one thickness of 24.64 A (Guo 2018). Guo 2018

How it is used

  1. Displace supercells

    Generate symmetry-reduced displacements of 0.03 A in supercells for fc2 and fc3.

  2. Compute forces

    Run the DFT code on every displaced supercell and collect the forces.

  3. Fit force constants

    Build fc2 and fc3 from the forces. Add the non-analytical correction from Born charges.

  4. Linewidths on a mesh

    Interaction strengths and imaginary self energies on a q mesh with the tetrahedron method.

  5. Conductivity

    Kappa by RTA or LBTE, mode lifetimes and cumulative kappa from kappa-mXXXXXX.hdf5.