Theoretical analysis of spectral lineshapes from molecular dynamics

Abstract

Conventional methods for calculating anharmonic phonon properties are computationally expensive. To address this issue, a theoretical approach was developed for the accelerated calculation of vibrational lineshapes for spectra obtained from finite-time molecular dynamics. The method gives access to the effect of anharmonicity-induced frequency shift and lifetime, as well as simulation broadening. For a toy model we demonstrate at least an order of magnitude reduction in the number of simulation steps needed to obtain converged vibrational properties in nearly all cases considered as compared to the standard extraction procedure. The theory is also illustrated for graphene, hexagonal boron nitride, and silicon at the density functional theory level, with up to nearly a factor of 9 reduction in the required simulation time to reach convergence in the vibrational frequencies and lifetimes. In general, we expect the newly developed method to outperform the standard procedure when the anharmonicity is sufficiently weak so that well-defined renormalized phonon quasiparticles emerge. Our extension of signal analysis to material vibrations represents a state-of-the-art advance in calculating temperature-dependent phonon properties and could be implemented in computational materials discovery packages that search for thermoelectric materials for instance, since the thermal conductivity contribution to ZT depends strongly on these characteristics.