Molecular orbital theory for infinite molecular aggregates: Application to idealized hexagonal and cubic ices

A single determinant molecular orbital theory for infinite molecular aggregates is developed. Calculations based on this theory are reported for idealized hexagonal and cubic ice structures in which the protons are ordered. The hexagonal structure is found to be the more stable by 0.75 kcal/mole. This stabilization is attributed in part to favourable three molecule interactions in the hexagonal lattice. The bond angles for the two independent sets of molecules in the idealized hexagonal ice structure are calculated to be 106.5° and 107.5°; the corresponding free molecule theoretical bond angle is 104.7°. The intermolecular charge transfer in the idealized hexagonal structure is calculated to be ∼10−5e. Intermolecular charge transfer in the cubic structure is symmetry forbidden