Derivation of a New Force Field for Crystal-Structure Prediction Using Global Optimization: Nonbonded Potential Parameters for Amines, Imidazoles, Amides, and Carboxylic Acids

Abstract

New nonbonded parameters of a “6-exp-1” all-atom force field are presented for amines, imidazoles, amides, and carboxylic acids. These results are part of our work to derive a general force field for the prediction of crystal and protein structures (the nonbonded parameters for aliphatic and aromatic hydrocarbons and alcohols were published recently, J. Phys. Chem. B 2003, 107, 7143). The parameters were derived by using our global-optimization-based method (J. Phys. Chem. B 2003, 107, 712) which provides the best possible set of parameters for crystal structure prediction for a given form of the potential. The method consists of two steps. First, an initial set of parameters is derived from ab initio quantum mechanical interaction energies of dimers; then, the initial set is refined to satisfy the following criteria: the parameters should reproduce the observed crystal structures and sublimation enthalpies, and the experimental crystal structure should correspond to the global minimum of the potential. The refinement procedure uses information about the potential energy surface of the crystal obtained by global energy minimization. Vector Monte Carlo (J. Phys. Chem. B 2003, 107, 712) and force-minimization methods are used in the refinement step. The parameters presented in this paper reproduce experimental crystal structures with high accuracy. The experimental structures of all molecules tested were found as the global or one of the lowest-energy minima of the potential.