Sara Bonella - Scaling up anharmonic (quantum) calculations of phonons

Abstract The analysis of lattice vibrations provides vital information on a variety of material properties and is of great experimental interest. Most of the available techniques and software tools to compute phonons rely on harmonic approximations of the classical ionic motion. When the material contains light ions or is subjected to temperatures and/or pressures deviating significantly from ambient conditions, anharmonic and quantum effects may alter its phonon characteristics. Simulating these effects, however, comes at a numerical cost still too high to model large systems within a first principle model of the interactions. Here, we present an approach that facilitates anharmonic quantum phonon calculations via accurate and relatively low cost ab initio molecular dynamics. We leverage the power of the recently introduced mass zero constrained dynamics in the orbital free DFT framework [1], together with a computational framework that relates anharmonic phonon spectra to time correlation functions [2]. Path integral and quantum thermal bath dynamics are employed and compared to incorporate quantum nuclear effects. References [1]A. Coretti, T. Baird, R. Vuilleumier, S. Bonella, The Journal of Chemical Physics, 157, (2022) [2]T. Morresi, L. Paulatto, R. Vuilleumier, M. Casula, J. Chem. Phys., 154, 224108 (2021) [3]M. Martinez, M. Gaigeot, D. Borgis, R. Vuilleumier, The Journal of Chemical Physics, 125, (2006)