Ab initio Calculation of Binding Energies of Interstellar
  Sulphur-Containing Species on Crystalline Water Ice Models
  There are different environments in the interstellar medium (ISM), depending
on the density, temperature and chemical composition. Among them, molecular
clouds, often referred to as the cradle of stars, are paradigmatic environments
relative to the chemical diversity and complexity in space. Indeed, there,
radio to far-infrared observations revealed the presence of several molecules
in the gas phase, while near-infrared spectroscopy detected the existence of
submicron sized dust grains covered by H2O -dominated ice mantles. The
interaction between gas-phase species and the surfaces of water ices is
measured by the binding energy (BE), a crucial parameter in astrochemical
modelling. In this work, the BEs of a set of sulphur-containing species on
water ice mantles have been computed by adopting a periodic ab initio approach
using a crystalline surface model. The Density Functional Theory (DFT)-based
B3LYP-D3(BJ) functional was used for the prediction of the structures and
energetics. DFT BEs were refined by adopting an ONIOM-like procedure to
estimate them at CCSD(T) level toward complete basis set extrapolation, in
which a very good correlation between values has been found. Moreover, we show
that geometry optimization with the computationally cheaper HF-3c method
followed by single point energy calculations at DFT to compute the BEs is a
suitable cost-effective recipe to arrive at BE values of the same quality as
those computed at full DFT level. Finally, computed data were compared with the
available literature data.
