title: Parallelization of a multiconfigurational perturbation theory.
abstract: In this work, we present a parallel approach to complete and restricted active space second-order perturbation theory, (CASPT2/RASPT2). We also make an assessment of the performance characteristics of its particular implementation in the Molcas quantum chemistry programming package. Parallel scaling is limited by memory and I/O bandwidth instead of available cores. Significant time savings for calculations on large and complex systems can be achieved by increasing the number of processes on a single machine, as long as memory bandwidth allows, or by using multiple nodes with a fast, low-latency interconnect. We found that parallel efficiency drops below 50% when using 8-16 cores on the shared-memory architecture, or 16-32 nodes on the distributed-memory architecture, depending on the calculation. This limits the scalability of the implementation to a moderate amount of processes. Nonetheless, calculations that took more than 3 days on a serial machine could be performed in less than 5 h on an InfiniBand cluster, where the individual nodes were not even capable of running the calculation because of memory and I/O requirements. This ensures the continuing study of larger molecular systems by means of CASPT2/RASPT2 through the use of the aggregated computational resources offered by distributed computing systems.
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200F, Heverlee B-3001, Belgium. steven.vancoillie@chem.kuleuven.be
authors.forename: Steven
authors.initials: S
authors.lastname: Vancoillie
authors.forename: Mickaël G
authors.initials: MG
authors.lastname: Delcey
authors.forename: Roland
authors.initials: R
authors.lastname: Lindh
authors.forename: Victor
authors.initials: V
authors.lastname: Vysotskiy
authors.forename: Per-Åke
authors.initials: PÅ
authors.lastname: Malmqvist
authors.forename: Valera
authors.initials: V
authors.lastname: Veryazov
mesh_terms: D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009942:Organometallic Compounds
keywords: CASPT2; high performance computing; multiconfigurational perturbation theory; parallellization