First Experiences with ab initio Molecular Dynamics on OpenPOWER: The Case of CPMD

In this article, we present the algorithmic adaptation and code re-engineering required for porting highly successful and popular planewave codes to next-generation heterogeneous OpenPOWER architectures that foster acceleration and high bandwidth links to GPUs. Here we focus on CPMD as the most representative software for ab initio molecular dynamics simulations. We have ported the construction of the electronic density, the application of the potential to the wavefunctions and the orthogonalization procedure to the GPU. The different GPU kernels consist mainly of fast Fourier transforms (FFT) and basic linear algebra operations (BLAS). The performance of the new implementation obtained on Firestone (POWER8/Tesla) is discussed. We show that the communication between the host and the GPU contributes a large fraction of the total run time. We expect a strong attenuation of the communication bottleneck when the NVLink high-speed interconnect will be available.