The research of R. Hardy is directed at extending and refining the theory of the structural and vibrational properties of crystalline and amorphous solids and to assisting his colleagues with simulations, both by developing models for the microscopic interactions in the materials considered and by designing appropriate simulation strategies. For example, thermally activated processes in nanoscale magnetic films have been simulated in collaboration with R. Kirby, while structural phase transitions in Langmuir monolayers were studied in a project with C. Eckhardt.
What is needed, but does not now exist, is a method for predicting the structural and thermal properties of solids that (1) is accurate, (2) is applicable from absolute zero to the melting temperature, and (3) does not require a major research project on a super computer for each new material considered. Anharmonicity causes problems at high temperatures, while quantum effects must be included at low temperatures. Of the methods satisfying the third criterion, those based on analytical approximations (e.g., lattice dynamics) typically fail at high temperatures, while those based on statistical approximations (e.g., molecular dynamics and Monte Carlo simulations) typically fail at low temperatures. Progress is being make in the search for methods that satisfy all three criteria. For example, a simple approximation based on the correlated factors theorem has been shown to be effective at all temperatures from absolute zero to melting by calculations on a standard test case. Work is currently underway to adapt this approximation for the study of amorphous solids and crystals of general structure. Also, it has been demonstrated that the traditional simulation techniques can be combined with the analytic approximations from lattice dynamics to give predictions that are accurate at all temperatures. This is expected to apply to all types of solids except those that remain intensely anharmonic near absolute zero.
Recent Key Publications
D. R. Swanson, R. J. Hardy, and C. J. Eckhardt, "Monte Carlo Simulation of the Solid to Super Liquid Phase Transition of Langmuir Monolayers Using Cross-Section Potentials," J. Chem. Phys. 99, 8194 (1993).
R. J. Hardy, M. A. Day, R. C. Shukla, and E. R. Cowley, "Uncorrelated-Factors Approximation and a Comparison of Theories for Predicting Thermal Properties: a Lennard-Jones Solid," Phys. Rev. B 49, 8732 (1994).
R. D. Kirby, J. X. Shen, R. J. Hardy, and D. J. Sellmyer, "Magnetization Reversal in Nanoscale Magnetic Films with Perpendicular Anisotropy," Phys. Rev. B 49, 10810 (1994).
Recent Graduates and Current Affiliations
David R. Swanson, Ph.D. 1995 (jointly with C. Eckhardt), currently a Fullbright Fellow Dissertation: "Quantitative Conceptual Models for Langmuir Monolayers