Solid state quantum mechanics

Application of Solid-state Quantum Mechanics to the Group 14 Elements... 

Advanced ab initio Methods, Density Functional Theory and Solid-state Quantum Mechanics... 

Based on the same underlying principles as the molecular-based quantum methods, solid state quantum mechanics represents bulk material using periodic boundary conditions. The imposition of these boundary conditions means that it becomes possible to expand the electron density in periodic functions such as plane waves, as an alternative to the atom-based functions used in the molecular case. The efficiency of the calculations is enhanced by the use of pseudo-potentials to represent the core electrons and to make the electron density as smooth as possible near the nucleus, hence reducing the complexity of the plane wave expansion of the electron density. Because of the number of choices available for pseudo potentials, basis sets and whether calculations are done in real or reciprocal space, there are many choices of software for performing solid state quantum mechanical calculations. A few examples which have been used in crystal structure prediction include the Vienna ab initio Simulation Package (VASP), CASTEP and CRYSTAL. " A wider ranging introduction to the area can be found in the references. ... 

Unbeknown to the participants of the first blind test, the crystal structures of two polymorphs of molecule I had been determined, a Plfc form and a meta-stable Pbca form. The latter form was predicted correctly by four participants, but the stable Plfc form was not found by any of the participants as one of their three predictions. Subsequent studies using molecular mechanics calculations to compute the lattice energies of the two polymorphs more accurately failed to obtain a satisfactory result for the stable form. Using solid state quantum mechanics, however, it was found that only about 0.1 kcal mol separates the calculated lattice energies of the two polymorphs, indicating that either form may be observed experimentally. ... 

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