| dc.description.abstract | Full-dimensional vibrational spectra are calculated for both X (H2O) and X (D2O) dimers (X = F, Cl,
Br, I) at the quantum-mechanical level. The calculations are carried out on two sets of recently developed
potential energy functions (PEFs), namely, Thole-type model energy (TTM-nrg) and many-body
energy (MB-nrg), using the symmetry-adapted Lanczos algorithm with a product basis set including
all six vibrational coordinates. Although both TTM-nrg and MB-nrg PEFs are derived from
coupled-cluster single double triple-F12 data obtained in the complete basis set limit, they differ
in how many-body effects are represented at short range. Specifically, while both models describe
long-range interactions through the combination of two-body dispersion and many-body classical electrostatics,
the relatively simple Born-Mayer functions employed in the TTM-nrg PEFs to represent
short-range interactions are replaced in the MB-nrg PEFs by permutationally invariant polynomials
to achieve chemical accuracy. For all dimers, the MB-nrg vibrational spectra are in close agreement
with the available experimental data, correctly reproducing anharmonic and nuclear quantum
effects. In contrast, the vibrational frequencies calculated with the TTM-nrg PEFs exhibit significant
deviations from the experimental values. The comparison between the TTM-nrg and MB-nrg results
thus reinforces the notion that an accurate representation of both short-range interactions associated
with electron density overlap and long-range many-body electrostatic interactions is necessary for
a correct description of hydration phenomena at the molecular level. | en |
