Can We Learn the Energy of Sublimation of Ice from Water Clusters?

TL;DR

This study calculates the electronic dissociation energies of water clusters using ab initio and potential models, finding a value close to the sublimation enthalpy of ice, which suggests a possible way to estimate ice sublimation energy from water cluster data.

Contribution

First-time calculation of dissociation energy per monomer for water clusters, showing convergence near 12 kcal/mol and linking it to ice sublimation energy.

Findings

Dissociation energy per monomer converges near 12 kcal/mol.

Estimated D0 value around 10-10.5 kcal/mol.

Close agreement with ice sublimation enthalpy of 10.2 kcal/mol.

Abstract

This short paper reports a study of the electronic dissociation energies, De, of water clusters from direct ab initio (mostly CCSD(T)) calculations and the q-AQUA and MB-pol potentials. These clusters range in size from 6-25 monomers. These are all in very good agreement with each other, as shown in a recent Perspective by Herman and Xantheas. To the best of our knowledge, we present for the first time results for the De per monomer. To our surprise this quantity appears to be converging to a value close to 12 kcal/mol. An estimate of 1.5 - 2 kcal/mol for the {\Delta}ZPE for these clusters puts the value of D0 at 10 to 10.5 kcal/mol. This value is remarkably (and probably fortuitously) close to the reported sublimation enthalpy of 10.2 kcal/mol at 10 K. However, given that these De energies correspond to dissociation of the cluster to N isolated monomers the interpretation of ``vaporization" of these ``solid" clusters is qualitatively reasonable.