The Perturbation Theory of Electron Correlation IV

Abstract

Computers play a central role in the practical applications of the vast majority of the apparatus of theoretical chemistry. Indeed, the outlook for performing quantum mechanical studies of the electronic structure of molecules changed radically in the 1950s with the advent of the electronic digital computer. Steady increase in the performance of these machines during the following decades was reflected in the increasing sophistication of computational techniques leading to higher precision in ab initio calculations and the ability to handle more extensive molecular systems. With the availability of vector processing computers, such as the CRAY 1 and CDC Cyber 205 in the late 70s, came a significant increase in performance; an improvement by a factor of 100 was observed in certain stages of electronic structure calculations. In more recent years, the trend in the development of computer architectures has been towards multiprocessor machines as exemplified by the CRAY X-MP and Y-MP computers. The successful exploitation of these new architectures requires that the effective algorithms be devised allowing parts of the computation to proceed concurrently [1–2].