Simulations of light induced processes in water based on ab initio path integrals molecular dynamics. II. Photoionization

Svoboda, Ondřej; Ončák, Milan; Slavíček, Petr

doi:doi:10.1063/1.3649943

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Simulations of light induced processes in water based on ab initio path integrals molecular dynamics. I. Photoabsorption

We have performed large-scale simulations of UV absorption spectra of water clusters (monomer to octamer) using a combination of ab initio path-integral molecular dynamics with reflection principle. The aim of the present work is four-fold: (1) To explore the transition from isolated molecules to bulk water from the perspective of UV photoabsorption. (2) To investigate quantum nuclear and thermal effects on the shape of the water UV spectra. (3) To make an assessment of the density functional th...

Accurate quantum mechanical study of the Renner-Teller effect in the singlet CH₂

The Renner-Teller (RT) effect between the two low-lying electronic states of singlet CH2, 1A1 and 1B1, is studied using the multi-configuration time-dependent Hartree method with complete treatment of the RT terms. The RT terms, which are the matrix elements of the electronic orbital angular momentum operators, are calculated with ab initio methods and fitted to analytical functions. The ro-vibronic energy levels with complete treatment and constant approximation of the RT terms are calculated a...

We have applied ab initio based reflection principle to simulate photoelectron spectra of small water clusters, ranging from monomer to octamer. The role of quantum and thermal effects on the structure of the water photoelectron spectra is discussed within the ab initio path integral molecular dynamics (PIMD) framework. We have used the PIMD method with up to 40 beads to sample the ground state quantum distribution at temperature T = 180 K. We have thoroughly tested the performance of various density functionals (B3LYP, BHandHLYP, M06HF, BNL, LC-ωPBE, and CAM-B3LYP) for the ionization process description. The benchmarking based on a comparison of simulated photoelectron spectra to experimental data and high level equation-of-motion ionization potential coupled clusters with singles and doubles calculations has singled out the BHandHLYP and LC-ωPBE functionals as the most reliable ones for simulations of light induced processes in water. The good performance of the density functional theory functionals to model the water photoelectron spectra also reflects their ability to reliably describe open shell excited states. The width of the photoelectron spectrum converges quickly with the cluster size as it is controlled by specific interactions of local character. The peak position is, on the other hand, defined by long-range non-specific solvent effects; it therefore only slowly converges to the corresponding bulk value. We are able to reproduce the experimental valence photoelectron spectrum of liquid water within the combined model of the water octamer embedded in a polarizable dielectric continuum. We demonstrate that including the long-range polarization and the state-specific treatment of the solvent response are needed for a reliable liquid water ionization description.

Article Outline

INTRODUCTION
METHODS
1. Photoionization spectrum
2. Electronic structure methods
RESULTS AND DISCUSSION
1. Assessment of electronic structure methods for water ionization
2. Quantum and thermal effects on PE spectra
3. Evolution of the PE spectra with the cluster size
4. Photoelectron spectra in solution: Hybrid approach
CONCLUSIONS AND OUTLOOK

EDITORIALLY RELATED

Simulations of light induced processes in water based on ab initio path integrals molecular dynamics. I. Photoabsorption
Ondřej Svoboda et al.
J. Chem. Phys. 135, 154301 (2011)JCPSA6000135000015154301000001

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KEYWORDS and PACS

Keywords

ab initio calculations, density functional theory, excited states, ground states, molecular clusters, molecular configurations, molecular dynamics method, molecular moments, molecule-photon collisions, photoelectron spectra, photoionisation, polarisability, spectral line breadth, water

PACS

36.40.Mr

Spectroscopy and geometrical structure of clusters
36.40.Cg

Electronic and magnetic properties of clusters
33.80.Eh

Autoionization, photoionization, and photodetachment
33.70.Jg

Line and band widths, shapes, and shifts
33.60.+q

Photoelectron spectra
31.15.ae

Electronic structure and bonding characteristics

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3649943

PUBLICATION DATA

ISSN

0021-9606 (print)

1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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