Optimization and performance of RMG DFT-based electronic structure software on exascale architectures

Exascale computer architectures are close to deployment, with several systems expected to come online within the next 1-2 years. Exploiting their full computational power to study challenging scientific problems requires careful attention to machine design and its interaction with the algorithms used in scientific codes. The RMG software package for electronic structure calculations has been optimized for pre-exascale machines such as Summit at ORNL, and we describe the work being done to port RMG to exascale-class machines. RMG uses a real-space formulation of the Kohn-Sham equations that map well to distributed node architectures via domain decomposition. However, using mixed CPU-GPU architectures efficiently requires careful work to hide or reduce the latencies associated with CPU-GPU and internodedata transfers. We discuss the methods used to address these issues in base RMG and those emerging when implementing advanced features, such as hybrid functionals, semi-local pseudopotentials, and spin-orbit coupling. Tests on AMD testbeds for the exascale Frontier show very promising performance. RMG source code and build scripts for pre-exascale Summit, Cray XE-XK, clusters, Linux, and Windows workstations are at www.rmgdft.org, together with help files and examples.