Extended symmetry-adapted discrete variable representation and acceleratedevaluation of (H)over-cap psi

It has long been realized that symmetry-adapted discrete variable represent ation for molecular systems with nontrivial symmetry leads to significant r eduction of the grid size, and thus computational costs. In this work, we s how that even for molecules with no symmetry it is still possible to achiev e significant computational savings by symmetry adaptation. The extended sy mmetry-adapted discrete variable representation takes advantage of the high er symmetry in a part of the total Hamiltonian denoted as the reference Ham iltonian, e.g., a kinetic energy operator. When the evaluation of its actio n constitutes the more expensive part of the calculation such as in discret e variable representation (DVR) based methods, significant savings may ensu e. Applications to several commonly used kinetic energy operators are discu ssed. Numerical tests in simple as well as realistic systems are carried ou t to demonstrate the efficiency of the method. (C) 1999 American Institute of Physics. [S0021-9606(99)30406-2].