Classical effective particle models and applications for semiconductors

Huang-Xin Wang, University of Pennsylvania


In this research work, group-IV semiconductors are used as a prototype for studying strong covalent systems by classical force fields. A new method is proposed to simulate the electronic contribution by introducing classical effective particles. This approach is shown to be a feasible way of including some aspects of chemical bonding in many-body quantum systems. It represents a general class of force fields that are useful in large scale simulations of materials. We propose three models for silicon and other tetrahedral semiconductors, in progressive accuracy: the tetrahedral rotator model (TRM), the classical effective particle (CEP) model, and the valence bond CEP (VBCEP) model. Lattice-dynamics information is used as the most reliable fitting data base to determine parameters in the potentials. With simple pair potentials, the VBCEP model is able to give excellent agreement to the experimental phonon data and elastic properties, comparable to the best lattice-dynamics models for the same systems. To give a broader description of this potential, the relative energies from ab initio calculations for certain crystal structures are used as additional fitting criteria. This allows the model to be applicable for the situations where the geometries deviate substantially from the ground states, or where the bonding is qualitatively different from the normal covalent bonds (e.g., the high-pressure phases, surfaces and clusters). Several computational methods are used, including Monte Carlo, molecular dynamics, nonlinear optimization, and special techniques to treat the problem of massless particles, for which we have developed the necessary complete computer codes. In the calculations of surface static and dynamical properties, we propose the semi-infinite cell description for surface geometry and phonon calculations. The applications of the three models include the statistical mechanical properties, various cluster geometries, structures and energetics of high pressure phases, point defects in solids, and surfaces reconstructions. From these results, the VBCEP model is compared favorably to other widely used potential models for silicon.

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Recommended Citation

Wang, Huang-Xin, "Classical effective particle models and applications for semiconductors" (1992). Dissertations available from ProQuest. AAI9235217.