Temperature-dependent effective third-order interatomic force constants from first principles

The temperature-dependent effective potential (TDEP) method is generalized beyond pair interactions. The second-and third-order force constants are determined consistently from ab initio molecular dynamics simulations at finite temperature. The reliability of the approach is demonstrated by calculations of the mode Gruneisen parameters for Si. We show that the extension of TDEP to a higher order allows for an efficient calculation of the phonon life time, in Si as well as in epsilon-FeSi; a system that exhibits anomalous softening with temperature.