Computational Screening of Weak Hydrogen Bond Networks: Predicting Stable Structures for Difluoromethane Oligomers

The stability and the structure of small difluoromethane oligomers are studied by combining classical Monte Carlo and quantum mechanical calculations. A hierarchical procedure was adopted to validate the accuracy of the whole protocol: the force field used in Monte Carlo simulations is parametrized on the basis of dimer intermolecular energies computed with density functional theory. The density functional is similarly chosen by comparing the interaction energies with reference values, purposely computed at a coupled cluster level, extrapolated at the complete basis set. The structures of dimers, trimers, and tetramers identified by the screening as local minima are first characterized by some geometrical parameters and by their dipole moment and eventually validated by comparison with results of microwave spectroscopy. The results are found in very good agreement with the experiment for all considered structures.