Ar _nHF van der Waals clusters revisited. I. New low-energy isomeric structures for n=6-13

New low-lying isomeric structures of Ar _nHF clusters are reported for n = 6-13. They were determined using simulated annealing and evolutionary programing, for pairwise additive intermolecular potential energy surfaces. New global minima were found for the clusters with n = 7, 10, 11. The new lowest-energy structure of Ar ₇HF and several new local minima for n = 6, 7 clusters have the HF bound on a threefold surface site, consistent with the recent spectroscopic data for Ar _nHF clusters in helium nanodroplets. A new type of low-energy local minima were determined for n = 9-13 clusters.