Self-consistent phonon calculations of lattice dynamical properties in cubic SrTiO$_{3}$ with first-principles anharmonic force constants

TL;DR

This paper introduces an ab initio self-consistent phonon method using anharmonic force constants to accurately compute lattice dynamical properties in highly anharmonic materials like cubic SrTiO3, including phonon frequencies, lifetimes, and thermal conductivity.

Contribution

The study develops an efficient, first-principles framework combining SCPH theory and anharmonic force constants to analyze strongly anharmonic systems, addressing limitations of previous harmonic approaches.

Findings

Successfully calculated phonon quasiparticles free of imaginary frequencies.

Revealed size dependence of anharmonic phonon frequencies near phase transition.

Predicted lattice thermal conductivity using phonon lifetimes and Boltzmann transport equation.

Abstract

We present an \textit{ab initio} framework to calculate anharmonic phonon frequency and phonon lifetime that is applicable to severely anharmonic systems. We employ self-consistent phonon (SCPH) theory with microscopic anharmonic force constants, which are extracted from density-functional calculations using the least absolute shrinkage and selection operator technique. We apply the method to the high-temperature phase of SrTiO$_{3}$ and obtain well-defined phonon quasiparticles that are free from imaginary frequencies. Here we show that the anharmonic phonon frequency of the antiferrodistortive mode depends significantly on the system size near the critical temperature of the cubic-to-tetragonal phase transition. By applying perturbation theory to the SCPH result, phonon lifetimes are calculated for cubic SrTiO$_{3}$, which are then employed to predict lattice thermal conductivity using the Boltzmann transport equation within the relaxation-time approximation. The presented methodology is efficient and accurate, paving the way toward a reliable description of thermodynamic, dynamic, and transport properties of systems with severe anharmonicity, including thermoelectric, ferroelectric, and superconducting materials.