Parallelization of Four-Component Calculations. I. Integral Generation, SCF, and Four-Index Transformation in the Dirac–Fock Package MOLFDIR

The treatment of relativity and electron correlation on an equal footing is essential for the computation of systems containing heavy elements. Correlation treatments that are based on four-component Dirac–Hartree–Fock calculations presently provide the most accurate, albeit costly, way of taking relativity into account. The requirement of having two expansion basis sets for the molecular wave function puts a high demand on computer resources. The treatment of larger systems is thereby often prohibited by the very large run times and files that arise in a conventional Dirac–Hartree–Fock approach. A possible solution for this bottleneck is a parallel approach that not only reduces the turnaround time but also spreads out the large files over a number of local disks. Here, we present a distributed-memory parallelization of the program package MOLFDIR for the integral generation, Dirac–Hartree–Fock and four-index MS transformation steps. This implementation scales best for large AO spaces and moderately sized active spaces