Lattice dynamics and thermal transport in layered KCuSe and RbCuSe: effects of phonon renormalization and four-phonon scattering

Abstract This paper employs first-principles calculations combined with self-consistent phonon theory and anharmonic lattice dynamics to investigate the lattice dynamics and thermal transport properties of layered KCuSe and RbCuSe. Temperature-dependent lattice thermal conductivity was calculated considering both three-phonon and four-phonon scattering. The results show that the lattice thermal conductivity of RbCuSe is lower than that of KCuSe, attributed to its lower phonon group velocity, larger scattering phase space, and stronger anharmonicity. Four-phonon scattering is comparable to three-phonon scattering and plays a crucial role in suppressing thermal transport. These results reveal the role of quartic anharmonicity in layered alkali metal copper selenides at the microscopic level and provide guidance for designing materials with intrinsically low lattice thermal conductivity.