David Oxtoby is supported by a grant from the Theoretical and Computational Chemistry Program to continue his work on nucleation theory. He will use statistical mechanical techniques, primarily density functional approaches, to investigate the dynamics of first-order phase transitions. Such transitions are of central importance in many areas of science and technology. The objective of the current research program is to develop new theoretical approaches to be able to predict nucleation rates for gas-liquid and liquid-solid phase transitions. The density functional approach used by Oxtoby incorporates atomic-level interactions to an extent not possible in traditional classical theories of nucleation. Specific targets of the research program for the next three years include: 1) a better understanding of the effects of dipolar interactions on nucleation; 2) a microscopic and predictive approach to the phase diagrams of three-component water-oil-surfactant systems that produce microemulsions; 3) an improved theory of crystal nucleation in metal alloys; 4) a new approach to protein crystallization and its relation to coagulation; and 5) a careful study of the effects of solid substrates and electric fields on crystal nucleation. Nucleation is important in a number of areas of science and technology including: 1) the condensation and freezing of water vapor in clouds; 2) the casting of solid metals and metal alloys from the melt; and 3) the growth of protein crystals from solution in order to determine their structure. On a molecular level, the mechanism of these changes of state are not well understood, and perhaps the least-understood aspect is the rate at which the first clusters of the new phase appear. This step, defined as nucleation, is often rate-determining for the formation of the new phase, and it is the step which Oxtoby's research will attempt to elucidate.