In this project funded by the Theoretical and Computational Chemistry Program of the Chemistry Division, Singer will perform mixed quantum/classical theoretical calculations on three systems of fundamental scientific interest and technological relevance: (1) the hydrated proton, (2) the catalytic site of zeolite, and (3) metal/rare gas clusters. He will also explore new theoretical methods for a simulated annealing treatment of many-electron solutes and electron- solvent pseudopotentials. %%% Many chemical processes, including those of living organisms, occur in water solution. Singer's work on the hydrated proton will pave the way for treating proton exchange reactions of such systems. His work on zeolites deals with the active site of a class of catalysts of vital importance in the petroleum industry. The new theoretical methods he seeks will be of value in future studies of chemical processes in solution.