Theoretical Studies of Silicon and Related Elements

Abstract

Abstract : On the theoretical side, a new highly scalable code for frozen core second order perturbation theory gradients for closed shell molecules has been developed. The development of analogous codes for molecules with unpaired electrons is in progress. A sequential unrestricted code for this purposed has been completed. The derivation for the spin-restricted open shell second order perturbation theory gradients has been completed, and a paper describing this derivation has now been accepted. Other important developments are new convergence methods for MCSCF wave functions that facilitate MCSCF calculations on large molecules, the derivation of gradients for multi-reference second order perturbation theory, the development and implementation of a full-CI method that is amenable to parallelization, further developments of our effective fragment potential (EFP) method for studying solvation and liquid behavior, the development of molecular dynamics and Monte Carlo methods to facilitate the study of solvation and liquid behavior, the development and implementation of a new method for producing global potential energy surfaces from sets of ab initio points, the development and implementation of both grid-based and gridless approaches to density functional theory, and the development and implementation of several MCSCF-based approaches to spin-orbit coupling. With regard to applications, considerable progress has been made in our understanding of the mechanisms for formation of POSS (polyhedral oligomeric silsesquioxanes) and the possibility of passing small gas molecules though them. POSS titanium analogs have also been studied, as have the hydrosilation and bis-silylation reactions. Other applications include studies of surface chemistry, several silicon systems and studies of the behavior of water clusters.