SEMIDIRECT MP2 GRADIENT EVALUATION ON WORKSTATION COMPUTERS - THE MPGRAD PROGRAM

A semidirect implementation of the closed-shell MP2 gradient for efficient use on workstation computers is presented. The approach is based on the algorithm proposed by Frisch and coworkers but includes several modifications to reduce disk storage requirements and exploits nonabelian point group symmetry. The performance of the resulting program MPGRAD (BIOSYM Corp., San Diego, CA) is demonstrated in applications to the molecules [AlSi(CH3)3]4 and ferrocene. The largest calculation involved 492 basis functions and was carried out on IBM RS/6000 workstations with memory sizes of 32 and 128 Mb. The ratio of CPU to wallclock time exceeds 90% in all typical applications. (C) 1993 by John Wiley & Sons, Inc.