Large-scale phonon calculations using the real-space multigrid method

Phonons are fundamental to understanding the dynamical and thermal properties of materials. However, first-principles phonon calculations are usually limited to moderate-size systems due to their high computational requirements. We implemented the finite displacement method (FDM) in the highly parallel real-space multigrid (RMG) suite of codes to study phonon properties. RMG scales from desktops to clusters and supercomputers containing thousands of nodes, fully supports graphics processing units (GPUs), including multiple GPUs per node, and is very suitable for large-scale electronic structure calculations. It is used as the core computational kernel to calculate the force constants matrix with FDM. By comparing with other widely used density functional theory packages and experimental data from inelastic neutron scattering, we demonstrate that RMG is very accurate in calculating forces at small displacements from equilibrium positions. The calculated phonon band structures and vibrational spectra for a variety of different systems are in very good agreement with plane-wave-based density functional theory codes, Quantum ESPRESSO, CASTEP and VASP, and these results have been validated comparing with inelastic neutron scattering experimental data measured at the VISION spectrometer at the Spallation Neutron Source.