An analysis of hydrogen-bonded systems: (HF)2, (H2O)2and H2O … HF

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Abstract
Within the context of extended geminal models, the concepts of charge centroids and charge ellipsoids of the geminal one-electron densities, and an energy decomposition of the intermolecular potential, are introduced as tools of analysis. The intermolecular potential can be written within this framework as a sum of distortion energies of the subsystems plus the interaction energies between the distorted subsystems. The interaction energy is further partitioned into Coulombic, exchange and correlation contributions. The main results of calculations on the dimers (HF)2, H2O … HF and (H2O)2, using a [7s, 4p, 2d/4s, 2p] contracted Gaussian-type basis set, are as follows. First, the equilibrium geometry of the dimers are strongly correlated with the location in space of the lone-pair charge ellipsoids of the proton acceptor. Secondly, the intermolecular potential is dominated by the Coulombic interaction energy and the distortion energies. However, these contributions have different signs, and, although the intersystem exchange and correlation terms are considerably smaller in magnitude, the latter terms make substantial contributions to the intermolecular potential.