Charge-transfer-to-solvent states provide a sensitive spectroscopic probe of the local solvent structure around anions

17 October 2022, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

This computational study characterizes charge-transfer-to-solvent (CTTS) states of aqueous thiocyanate anion using equation-of-motion coupled-cluster methods combined with electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) scheme. Equilibrium sampling was carried out using classical molecular dynamics (MD) with standard force-fields and QM/MM ab initio molecular dynamics (AIMD) using density functional theory. The two calculations yield significantly different local structure around solvated SCN−. Because of the diffuse character of CTTS states, they are very sensitive to the local structure of solvent around the solute and its dynamic fluctuations. Owing to this sensitivity, the spectra computed using MD and AIMD based snapshots differ considerably. This sensitivity suggests that the spectroscopy exploiting CTTS transitions can provide an experimental handle for assessing the quality of force-fields and density functionals. By combining CTTS-based spectroscopies with reliable theoretical modeling, detailed microscopic information of the solvent structure can be obtained. We present a robust computational protocol for modeling spectra of solvated anions and emphasize the use of an ab initio characterization of individual electronic transitions as CTTS or local excitations.

Keywords

QM/MM
AIMD
Anion solvation
UV Spectroscopy
Charge transfer to solvent
Molecular Dynamics
Wave-function analysis

Supplementary materials

Title
Description
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Title
Charge-transfer-to-solvent states provide a sensitive spectroscopic probe of the local solvent structure around anions: Supplementary Information
Description
Details of protocol development for EOM-EE calculations and calculation setup.
Actions

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