Ab initio variational approach for evaluating lattice thermal conductivity

TL;DR

This paper introduces a first-principles variational method for accurately calculating lattice thermal conductivity, improving computational efficiency and convergence, with applications demonstrated on diamond.

Contribution

It presents a novel variational approach using conjugate gradient for lattice thermal conductivity calculation, ensuring exact solutions and enhanced speed over previous methods.

Findings

Method achieves better convergence and speed.

Accurate modeling of phonon scattering processes.

Potential to increase thermal conductivity in isotopically enriched diamond.

Abstract

We present a first-principles theoretical approach for evaluating the lattice thermal conductivity based on the exact solution of the Boltzmann transport equation. We use the variational principle and the conjugate gradient scheme, which provide us with an algorithm faster than the one previously used in literature and able to always converge to the exact solution. Three-phonon normal and umklapp collision, isotope scattering and border effects are rigorously treated in the calculation. Good agreement with experimental data for diamond is found. Moreover we show that by growing more enriched diamond samples it is possible to achieve values of thermal conductivity up to three times larger than the commonly observed in isotopically enriched diamond samples with 99.93% C12 and 0.07 C13.