Benchmarking Ab Initio Binding Energies of Hydrogen-Bonded Molecular Clusters Based on FTIR Spectroscopy

Abstract

Models of formation and growth of atmospheric aerosols are highly dependent on accurate cluster binding energies. These are most often calculated by ab initio electronic structure methods but remain associated with significant uncertainties. We present a computational benchmarking study of the Gibbs free binding energies in molecular complexes and clusters based on gas phase FTIR spectroscopy. The acetonitrile-HCl molecular complex is identified via its redshifted H-Cl stretching vibrational mode. We determine the Gibbs free binding energy, ΔG°295 K, to between 4.8 and 7.9 kJ mol(-1) and compare this range to predictions from several widely used electronic structure methods, including five density functionals, Møller-Plesset perturbation theory, and five coupled cluster methods up to CCSDT quality, considering also the D3 dispersion correctional scheme. With some exceptions, we find that most electronic structure methods overestimate ΔG°295 K. The effects of vibrational anharmonicity is approximated using scaling factors, reducing ΔG°295 K by ca. 1.8 kJ mol(-1), whereby ΔG°295 K predictions well within the experimental range can be obtained.

Computational approaches for efficiently modelling of small atmospheric clusters

“…Based on recent benchmarks, we utilize the DFT functionals M06-2X, PW91 and ωB97X-D, which have been identified to perform well in describing clusters of atmospheric relevance [19,20,[24][25][26]. While these three functionals show relatively similar performance they are constructed very differently.…”

The effect of large amplitude motions on the vibrational intensities in hydrogen bonded complexes

“…[14][15][16][17][18][19][20][21][22] With this method, equilibrium constants of complex formation are determined from the definition of the equilibrium constant…”

Control of a photoswitching chelator by metal ions:DFT,NBO, andQTAIManalysis

“…A more detailed analysis of vibrational properties would involve inclusion of anharmonicity, which would most likely result in construction of high‐dimensional models. This is usually the case for systems with bridges that connect distinct atoms, like in hydrogen bonded systems …”