Quantum Mechanics/Molecular Mechanics Modeling of Photoelectron Spectra: The Carbon 1s Core–Electron Binding Energies of Ethanol–Water Solutions

Abstract

Using ethanol-water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute-solvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics model-electrostatic, polarization, and van der Waals-with atom or bond granulation of the corresponding MM charge and polarizability force-fields. The role of extramolecular charge transfer screening of the core-hole and explicit hydrogen bonding is studied by extending the QM core to cover the first solvation shell. The results are compared to those obtained from pure electrostatic and polarizable continuum models. Particularly, the dependence of the carbon 1s binding energies with respect to the ethanol concentration is studied. Our results indicate that QM/MM can be used as an all-encompassing model to study photoelectron binding energies and chemical shifts in solvent environments.

Universal Calibration of Computationally Predicted N 1s Binding Energies for Interpretation of XPS Experimental Measurements

“…Some of these challenges are described in a very detailed study by Löytynoja et al of the C 1s electron binding energies in water–ethanol solutions. 17 At the same time, these absolute energy comparisons are what would make the computational predictions a universal measuring stick for a wide variety of chemical systems on a wide variety of solid substrates. The work and motivations described below are building on the successful and highly practical correlation procedure offered by Zuilhof group for C 1s energies and XPS measurements for surface species in 2013 18 and the exploratory correlations offered for N 1s energies and surface spectroscopy studies by the groups of Zuilhof 18 and Teplyakov.…”

“…However, while the differences between the core level energies in species with different chemical environments (core level shifts) are typically sufficiently and reliably predicted in this way, prediction of the absolute binding energies has presented a number of challenges. Some of these challenges are described in a very detailed study by Löytynoja et al of the C 1s electron binding energies in water–ethanol solutions . At the same time, these absolute energy comparisons are what would make the computational predictions a universal measuring stick for a wide variety of chemical systems on a wide variety of solid substrates.…”

Experimental observation of structural phase transition in CsBr clusters

“…Structures of single CsBr monomer and CsBr in Ar cluster were optimized with the Gaussian program [31] using density functional theory (DFT) with D3 version of Grimme's dispersion with Becke-Johnson damping [32] on def2-TZVP [33,34]/B3LYP [35] level of theory. Br 3d and Cs 4d binding energies were calculated with the Dalton program [36] using the -DFT method [37,38]. The calculations were performed using two groups of basis sets: (i) DZP [39,40] for Cs and def2-TZVP for Br and (ii) def2-TZVP basis for both.…”

Exploring the Solvation of Acetic Acid in Water Using Liquid Jet X-ray Photoelectron Spectroscopy and Core Level Electron Binding Energy Calculations

“…This combined approach can be used for systematic study of microsolvation effects. It is well-established that valence 19 and core 20 ionization potentials converge very slowly with the number of solvent molecules surrounding the solute. Here, we used a combination of continuum solvation models and ab initio MD (AIMD) to speed up the convergence of the CEBEs.…”