The existence of multiple levels of description of a physical system was exploited in order to accelerate the determination of thermodynamic quantities. The technique was used to feed information, from an interatomic potential, into otherwise inaccessible quantum-mechanical tight-binding calculations of the reconstruction of partial dislocations in Si. It was concluded that there were enormous advantages in separating thermal studies of some systems into the exploration of phase-space (using a simpler coarse-grained Hamiltonian), and the use of a more detailed Hamiltonian to study the behavior of the system at a limited number of well-chosen points in phase-space. The approach worked well for the determination of the free energies of defects, using quantum-based calculations. As the system size increased, the determination of such local defects was relatively stable. Global changes, in which the observable of interest was correlated with the entire system, might require a different approach. A thermal quantum-mechanical description of the 30º partial dislocation core yielded a free energy of reconstruction which was significantly lower than previous Stillinger-Weber values, and thus led to a more consistent view of dislocation mobility in Si.

T.D.Engeness, T.A.Arias: Physical Review Letters, 1997, 79[16], 3006-9