Classical and quantum computer simulation studies; molecular dynamics of the Kerr effect in carbon disulfide and Green's function Monte Carlo calculations of the electronic correlation energy in atoms

This thesis research consists of computer simulation studies of both classical and quantum many body problems. The classical problem deals with the ultrafast Kerr effect observed in molecular liquids when irradiated with high intensity picosecond laser light. A strong birefringence is induced in such a system, and this study investigates the dynamics of that response. By using the molecular dynamics simulation method to integrate Newton's equations of motion for a large ensemble of molecules, these exact simulation results to predictions from diffusion theory. The second area of investigation addresses several issues concerning the applicability of quantum simulation methods to the calculation of electronic ground state properties of atoms and molecules. There exists a fundamental problem in applying quantum simulation methods in fermion systems. Approximate attempts by earlier researchers have been sufficiently flawed so as to make the significance of their results ambiguous. The author reexamines the application of the Green's Function Monte Carlo method to a class of lithium-like atoms in such a way as to systematically remove the major approximations from the method. The result yields a highly accurate and reliable approach to calculation ground state properties of atoms and molecules. Specific results for three electron atoms can be compared to other theoretical calculations and experiments