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Determination of the crystalline structure of nonlinear molecules in a combined quantum chemical and classic lattice potential description



The general problem of the prediction of the crystal parameters and molecular structure of nonlinear molecules is taken up in a treatment that couples the molecular electronic structure determination to the surrounding crystalline lattice field. The molecular electronic structure method used may be at any level of sophistication, but we used the Hartree–Fock approximation in this application. A partial charge analysis of the molecular electronic structure is performed to establish the values of atom-centered partial charges that interact via Coulomb's law, along with a Lennard–Jones potential between all atoms to establish a crystalline lattice field. The Lennard–Jones parameters are taken from the widely used AMBER force field. The lattice field terms are included in the molecular Hamiltonian and exert forces on the nuclei, leading to a somewhat different equilibrium structure than is obtained for the isolated molecule. The positions, orientations, and unit cell parameters are optimized for the lattice field, leading to a full determination of the crystal structure, including the space group. Results for sulfur dioxide, ammonia, and water are reported. In each case an equilibrium crystalline geometry faithfully reproducing the experimentally determined space group is obtained. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003