Abstract
Parallel implementation of an iterative determination of energy levels of large molecular systems is presented. The basic step consists in acting the Hamiltonian operator H on a wavefunction u, and is achieved by means of a Pseudo Spectral Split Hamiltonian scheme (C.leforestier et al.,J.Chem.Phys.,106,8527(1997)). The potential term evaluation V.u, which corresponds by far to the most time consuming part in the sequential code, has been distributed over all the processors. Application to the water dimer (H 2 O) 2 Vibration-Rotation spectrum shows a very good parallel efficiency up to 64 processors.