Assignment of photoelectron spectra of halide–water clusters: Contrasting patterns of delocalization in Dyson orbitals

Electron Propagator Theory of Vertical Electron Detachment Energies of Anions: Benchmarks and Applications to Nucleotides

A new generation of ab initio electron-propagator self-energy approximations that are free of adjustable parameters is tested on a benchmark set of 55 vertical electron detachment energies of closed-shell anions. Comparisons with older self-energy approximations indicate that several new methods that make the diagonal self-energy approximation in the canonical Hartree-Fock orbital basis provide superior accuracy and computational efficiency. These methods and their acronyms, mean absolute errors (in eV), and arithmetic bottlenecks expressed in terms of occupied (O) and virtual (V) orbitals are the opposite-spin, non-Dyson, diagonal second-order method (os-nD-D2, 0.2, OV²), the approximately renormalized quasiparticle third-order method (Q3+, 0.15, O²V³) and the approximately renormalized, non-Dyson, linear, third-order method (nD-L3+, 0.1, OV⁴). The Brueckner doubles with triple field operators (BD-T1) nondiagonal electron-propagator method provides such close agreement with coupled-cluster single, double, and perturbative triple replacement total energy differences that it may be used as an alternative means of obtaining standard data. The new methods with diagonal self-energy matrices are the foundation of a composite procedure for estimating basis-set effects. This model produces accurate predictions and clear interpretations based on Dyson orbitals for the photoelectron spectra of the nucleotides found in DNA.

Evaluation of Ar tagging toward the vibrational spectra and zero point energy of X-HOH, X-DOH, and X-HOD, for X = F, Cl, Br

In this study, we theoretically evaluated the effect of argon tagging toward the binding energy and vibrational spectra of water halide anion complexes Ar.X-HOH, Ar.X-HOD, and Ar.X-DOH (X = F, Cl, Br). The ionic hydrogen bond (IHB) OH stretching mode was calculated to have a strong peak in the vibrational spectra, and coupling to intermolecular modes as well as bending modes was observed as combination bands and Fermi resonances. We found that the argon tagging affected the IHB OH stretching peak position in Ar.F-H2O, but not in Ar.Cl-H2O and Ar.Br-H2O. Furthermore, D-binding is favored for Cl and Br based on zero point energies, but for F our calculated zero point energies did not show a preference between H- and D-binding. We show that the competition of the energy lowering in the zero point energy of the anharmonic IHB OH (OD) stretching mode versus the intermolecular out-of-plane IHB OH (OD) wagging mode is important for determining the preference between H- and D-binding for these monohydrated halide clusters. We also found that for X-HOD the HOD bending fundamental peak is blue shifted compared to bare HOD, but is redshifted for F-DOH.

Theoretical calculation of the vibrational state dependent photodetachment spectra of X-H2O, X = F, Cl, Br

Vibrational spectra of X^-H₂O (X = F, Cl, Br) were simulated using full dimensional vibrational calculations using quantum chemistry potential energy surfaces. Furthermore, utilizing the reflection approximation, we simulated the photodetachment spectra obtained from different vibrational excited states. From these spectra, we can observe changes in the hydrogen bond interaction between the anion and the neutral XH₂O system. Notably, for F^-H₂O, the excitation of the ionic hydrogen bonded (IHB) OH stretching vibration generates a large tail on the low energy side of the photodetachment spectra compared to the detachment from the zero-point vibration state. This shows that the IHB OH stretching vibration of F^-H₂O causes charge delocalization from F^- to the oxygen atom in H₂O, and that the photodetachment from FHOH^- occurs at lower energies.