High-Throughput Phonon Calculations With the Real-Space Multigrid Method (RMG)

We have combined our real-space multigrid code (RMG, www.rmgdft.org) with Phonopy to enable phonon calculations on large systems, up to ~1000 atoms, within the framework of Density Functional Theory. RMG is a real-space multigrid method based code for electronic-structure calculations, which is highly parallel with excellent scalability to thousands of nodes and GPUs. Phonopy is an open-source python-based package for pre/post-processing for phonon calculations with interfaces to many DFT codes. Employing the Finite Displacement Method (FDM), we build supercells with small perturbations from atoms’ equilibrium positions and perform self-consistent calculations to obtain interatomic forces in real space, which are transformed to reciprocal space to form dynamical matrices at arbitrary q values. Several techniques that reduce the computational cost or numerical errors and improve accuracy of the final results will also be discussed. We have used RMG for a variety of systems, four of which will be discussed in detail here: silicon, ZrH2, carbazole and ZIF-8. RMG’s results are also compared with inelastic neutron scattering data, measured at the VISION spectrometer at the SNS in ORNL, and other DFT codes for validation purposes.