AMOEBA force field parameterization of the azabenzenes

Abstract: We present an extension of the AMOEBA force field to several common organic heterocycles, namely pyridine, pyrazine, pyrimidine, pyridazine, the three unique triazines, and the two unique tetrazines. Atomic multipoles for newly defined atom types were obtained from quantum chemical calculations on the isolated molecules. Atomic polarizability parameters are maintained at their standard AMOEBA values for corresponding atomic classes while standard van der Waals parameters are rescaled to reproduce CCSD(T) intermolecular interaction energies of selected dimer structures. In order to improve vibrational frequencies that are important both spectroscopically and for flexible dynamics, parameters for covalent terms, i.e., bond-stretching, angle-bending, and stretch-bend terms, were optimized and added to the existing AMOEBA force field. We validate our force field through comparison of molecular structural, vibrational, electrostatic, and energetic properties—including intermolecular interaction energies—to reliable quantum chemical data for the various systems of interest.