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The knowledge of the binding energy of molecules on astrophysically relevantices can help to obtain an estimate of the desorption rate, i.e. the moleculesresidence time on the surface. This represents an important parameter forastrochemical models, crucial to determine the chemical fate of complex organicmolecules formed on dust grains and observed in the densest regions of theinterstellar medium. In this work, we propose a new robust procedure to studythe interaction of atoms and molecules with interstellar ices, based on\textit{ab initio} molecular dynamics and density functional theory, validatedby high-level \textit{ab initio} methods at a CCSD(T)/CBS level. We haveapplied this procedure to hydrogen fluoride (HF), a promising tracer of themolecular content of galaxies. In total we found 13 unique equilibriumstructures of HF binding to small water clusters of up to 4 molecules, withbinding energies ranging from 1208 to 7162 K. We computed a 22-molecules modelof amorphous solid water (ASW) surface using \textit{ab initio} moleculardynamics simulations and carried out a systematic analysis of the binding sitesof HF, in terms of binding modes and binding energies. Considering 10 differentwater clusters, we found a binding energy distribution with an average value of$5313\pm74$ K, and a dispersion of $921\pm115$ K. Finally, the effect of theelectrostatic field of the 22 water molecules on the binding energies wasinvestigated incrementally by symmetry adapted perturbation theory, in order togauge the effect of the water environment. The results indicate that the extentof the electrostatic interaction of HF with ASW depends strongly on theproperties of the binding site. We expect that this work will provide a solidfoundation for a systematic development of a binding energy distributiondatabase of molecules on interstellar surfaces.

High level ab initio binding energy distribution of molecules on interstellar ices: Hydrogen fluoride