The focus of attention for the ab initio procedures is the coupled- cluster method. This method, based on the notion that the physically most important part of the interactions between electrons can be described in terms of effects inherently involving but few particles at a time, is proving remarkably successful in a variety of atomic and molecular contexts. Work now in progress is extending the range of applicability of the method to extended systems, such as crystals and surfaces, and to unstable systems such as the intermediate states in collisional processes. Semi-empirical methods are being examined in attempts to improve their reliability while minimizing computational effort. The present state of ab initio calculations suggests that for some time to come it will be prohibitively costly to treat most larger chemical systems by precise methods and that approximate procedures will continue to be of great practical importance.
Work is currently in progress on two projects.
The focus of effort is on the removal of additional approximations ordinarily used to simplify the application of the X-alpha method to polyatomic molecules. An important aspect of formal development is the reduction of methods to practice by the production of appropriate computer programs. Emphasis is placed on the creation of quality scientific software so that, to a maximum extent, programs are modular, portable, well documented and written in ways facilitating understanding. The major thrust of our current software effort is in the development and implementaton of algorithms for use in massively parallel computing environments. Studies of specific systems are, for the most part, done in collaboration with research groups having needs for electronic structure information.