Exascale Electronic Structure and Quantum Transport Calculations

The creation of robust, adaptive software and algorithms that can fully exploit exascale capabilities and future computing architectures is critical to designing advanced materials and devices with targeted properties. We have developed an open-source code that discretizes the DFT equations on real-space grids distributed over the nodes of a massively parallel system via domain decomposition. Multigrid techniques are used to greatly accelerate convergence while only requiring nearest neighbor communications, while a novel adaptive finite differencing scheme dramatically improves accuracy. The real-space multigrid (RMG) code achieves the same average accuracy as plane wave codes on the well-known Delta test for 71 elements in the periodic table and can handle all Bravais lattice types. It scales from desktops and clusters to supercomputers, including the exascale Frontier and pre-exascale Summit, Perlmutter and Polaris systems, while utilizing all CPU cores and GPUs in each node. RMG is distributed via www.rmgdft.org, with over 4,000 downloads to date. Due to its computational efficiency, RMG is very suitable for large-scale survey approaches, including Materials-Genome and Machine-Learning projects. Advanced functionalities are provided through interfaces to other codes, including QMCPACK, BerkeleyGW, Phonopy, and ALAMODE. A localized-orbitals RMG module enables high-accuracy calculations with much-reduced memory footprint and scaling, saving 90% of wave function memory in 1,000-atom supercells. It forms the basis for a non-equilibrium Green’s function module able to study quantum transport properties for devices containing tens of thousands of atoms with full DFT accuracy. Several large-scale applications will be discussed.

*In collaboration with E. L. Briggs and W. Lu.