Flexible multipole models for hydrogen fluoride

We use the distributed multipole analysis method to analyse the charge density of the hydrogen fluoride molecule, including variation of the HF bond length, and taking into consideration the level of theory, the basis set, and the number of sites used. We also examine the effects of truncating the dimer electrostatic interactions at charge–charge, quadrupole–quadrupole and all interactions up to r−5 dependence in the intermolecular site–site separations. We assess the accuracy of these approximations using both the calculated multipoles and multipoles described by polynomial functions of the bond stretching coordinate. We consider two ranges of the HF bond length, one of which should be suitable for calculations of structures and energetics of hydrogen fluoride clusters, and the other for dynamical calculations on the same systems.