Parallelization of analytical Hartree±Fock and density functional theory Hessian calculations. Part I: parallelization of coupled- perturbed Hartree±Fock equations

Solving the coupled-perturbed Hartree±Fock (CPHF) equations is the most time consuming part in the analytical computation of second derivatives of the molecular energy with respect to the nuclei. This paper describes a unique parallelization approach for solving the CPHF equations. The computational load is divided by the nuclear perturbations and distributed evenly among the computing nodes. The parallel algorithm is scalable with respect to the size of the molecule, i.e. the larger the molecule, the greater the parallel speedup. The memory storage requirements are also distributed among the processors, with little communication among the processors. The method is implemented in the Q-Chem software package and its performance is discussed. This work represents the ®rst step in a research project to parallelize analytical frequency calculations at Hartree±Fock and density functional theory levels.