H/D isotope effect on structures, binding energies, and basis set superposition errors in F⁻(H₂O)_n (n = 1–3) clusters

Highlights: • We calculated the stabilities of F⁻(H₂O)_n (n = 1–3) clusters by MC_MO-MP2 method. • Our MC_MO-MP2 calculations revealed H/D geometrical isotope effects on the systems. • Nuclear quantum nature has significant effect on the binding energies. • BSSE changes the order of stability of F⁻(H₂O)₃ isomers in MC_MO-MP2 calculations. - Abstract: The H/D isotope effects on structures, binding energies, and basis set superposition errors (BSSEs) of hydrated fluoride anion clusters, F⁻(H₂O)_n (n = 1–3), are theoretically analyzed by using the MP2 level of multi-component molecular orbital (MC_MO-MP2) method, in which quantum nature of proton/deuteron and electron–electron correlation are directly taken account. Our results clearly show that the additional water molecule to F⁻(H₂O)_n−1 cluster forms stronger water–water hydrogen bond than that in simple water cluster, whereas the additional F⁻–water hydrogen bond formation in F⁻(H₂O)_n cluster weakens the original F⁻–water hydrogen bonds in F⁻(H₂O)_n−1 cluster. The BSSEs estimated in the MC_MO-MP2 calculations are slightly larger than those in the conventional MP2 calculations, due to the H/D geometrical isotope effect on the intermolecular distances. Consequently, the order of stability in several F⁻(H₂O)₃ cluster isomers cannot be adequately evaluated without BSSE corrections in our MC_MO-MP2 calculations, rather than the conventional MP2 ones