Energy Minimisation and Simulated Annealing Techniques

The simulation of structures using pair potential methods gives important information, including unit cell dimensions, atomic positions and details of atomic motion including lattice vibrations (phonon modes). Further analysis permits the calculation of heat capacities, the dependence of volume with temperature and the prediction of vibrational spectra, such as IR and neutron spectroscopies. Codes that perform such periodic structure energy minimisation using pair potential models include METAPOCS, THBREL and GULP (Table 4.1). All have been used successfully to model framework structures. 

Such calculations also successfully predict the observed variation of unit cell volume with temperature for zeolitic structures, including the effect of negative thermal expansivity. This latter effect results from the motion of essentially rigid tetrahedra that can result in the decrease of average distances between tetrahedral cations. Other applications of energy minimisa tion studies are given below. 

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