Theory of high-temperature superconductivity. We are conducting quantum Monte Carlo simulation of tight-binding models which support superconductivity. We have shown for example that the two-dimensional Little model indeed exhibits superconductivity induced by excitonic excitation. Simulation of some phenomenological models of d-wave superconductivity is yielding very interesting results.
The X-ray phase problem A fundamental problem in X-ray crystallography is to invert the diffraction data to determine the atomic positions in the crystals. We have been pursuing a new approach to solve this problem. An initial random guess of the atomic positions is gradually improved (by employing the technique of simulated annealing) until a sensible structure emerges. We have recently solved a molecular structure which has defied existing methods
