Towards Exascale Quantum Transport Calculations

Beyond Moore’s law devices will approach nanometer dimensions and operate in the regime where quantum and atomic-scale effects become important. In this regime, classical concepts of device design cease to be predictive and need to be augmented by quantum simulations of key parts of devices and circuits. Based on the non-equilibrium Green’s function (NEGF) methodology within the density functional theory, we have developed a NEGF module within the real-space multigrid (RMG) suite of codes (www.rmgdft.org) by which the quantum transport properties can be studied for nanoscale devices containing tens of thousands of atoms. Multilevel parallelization with MPI, threads and/or Cuda programming is implemented to enable adaptation to future exascale supercomputers. The module can be used to simulate and design new quantum devices at the atomic level. For a system with ten thousand atoms, the NEGF module’s performance scales linearly from 100 to 1000 nodes on the Summit supercomputer at ORNL. With an efficient implementation of GPU acceleration using the new Cuda-managed memory capability, our benchmark calculations show a 3.5 to 4.5 speed-up over CPU-only calculations.