First-principles study on the lattice dynamics and thermodynamic properties of Cu ₂ GeSe ₃

The lattice dynamics and thermodynamic properties of Cu2GeSe3 are investigated by first-principles calculations. The obtained phonon frequencies agree well with the measurements of Raman scattering. The thermodynamic properties are calculated within quasi-harmonic approximation, and the measured lattice thermal conductivity is well reproduced. The calculated Grüneisen parameter is found to be much smaller than previous prediction, indicating that the bonding anharmonicity is insufficient to explain the low thermal conductivity in Cu2GeSe3. Our study shows that the thermodynamic properties of Cu2GeSe3 are inherently related to its weak covalent Cu-Se bonding.