(545d) Ab Initio Crystal Structure Determination Using Global Optimization

Crystal structure determination is important to the understanding of the structure-function relationship in many branches of theoretical and applied chemistry. In this presentation, an ab initio global optimization method for crystal structure determination based on the terrain/funneling method is described. The global optimization formulation is comprised of a large constrained optimization problem, in which the objective function is an all-atom description of the potential energy and expressed in terms of the fractional coordinates of all atoms in the crystal and lattice parameters, and where the constraints remove translational and rotational symmetries and enforce bounds on variables. The key features of the proposed approach are that it is truly ab initio since random starting molecular and crystal configurations are used and the terrain/funneling method simultaneously adjusts both the conformation of each molecule as well as the packing of all molecules in the crystal. Numerical results for several crystal structure determination examples are presented that clearly show that the terrain/funneling method is a robust, reliable and efficient methodology for crystal structure determination, can handle polymorphism, solve large dimensional problems, and does not get trapped at local minima. Many geometric illustrations are used to elucidate key points.