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Title: Ab Initio Computation of Rotationally-Averaged Pump–Probe X-ray and Electron Diffraction Signals

Abstract

We develop a new algorithm for the computation of the rotationally averaged elastic molecular diffraction signal for the cases of perpendicular or parallel pump–probe geometries. The algorithm first collocates the charge density from an arbitrary ab initio wave function onto a Becke quadrature grid [A. Becke, J. Chem. Phys. 1988, 88, 2457], providing a high-fidelity multiresolution representation of the charge density. A double sum is then performed over the Becke grid points, and the interaction between points computed using the scattering kernels of Williamson and Zewail [J. C. Williamson and A. H. Zewail, J. Phys. Chem. 1994, 98, 2766]. These kernels analytically average over the molecular orientations with the cos 2γ selection factor appropriate for one-photon dipole absorption in a perpendicular pump–probe geometry. We demonstrate that the method is converged with small grids containing <500 points/atom. We implement the algorithm on a GPU for increased efficiency and emonstrate the algorithm for molecules with up to a few dozen atoms. We explore the accuracy of the independent atom model (IAM) by comparison with our new and more accurate method. We also investigate the possibility of detecting signatures of electronic transitions in polyatomic pump–probe diffraction experiments.

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Stanford Univ., CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1527342
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Theory and Computation
Additional Journal Information:
Journal Volume: 15; Journal Issue: 3; Journal ID: ISSN 1549-9618
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English

Citation Formats

Parrish, Robert M., and Martínez, Todd J. Ab Initio Computation of Rotationally-Averaged Pump–Probe X-ray and Electron Diffraction Signals. United States: N. p., 2019. Web. doi:10.1021/acs.jctc.8b01051.
Parrish, Robert M., & Martínez, Todd J. Ab Initio Computation of Rotationally-Averaged Pump–Probe X-ray and Electron Diffraction Signals. United States. doi:10.1021/acs.jctc.8b01051.
Parrish, Robert M., and Martínez, Todd J. Thu . "Ab Initio Computation of Rotationally-Averaged Pump–Probe X-ray and Electron Diffraction Signals". United States. doi:10.1021/acs.jctc.8b01051.
@article{osti_1527342,
title = {Ab Initio Computation of Rotationally-Averaged Pump–Probe X-ray and Electron Diffraction Signals},
author = {Parrish, Robert M. and Martínez, Todd J.},
abstractNote = {We develop a new algorithm for the computation of the rotationally averaged elastic molecular diffraction signal for the cases of perpendicular or parallel pump–probe geometries. The algorithm first collocates the charge density from an arbitrary ab initio wave function onto a Becke quadrature grid [A. Becke, J. Chem. Phys. 1988, 88, 2457], providing a high-fidelity multiresolution representation of the charge density. A double sum is then performed over the Becke grid points, and the interaction between points computed using the scattering kernels of Williamson and Zewail [J. C. Williamson and A. H. Zewail, J. Phys. Chem. 1994, 98, 2766]. These kernels analytically average over the molecular orientations with the cos2γ selection factor appropriate for one-photon dipole absorption in a perpendicular pump–probe geometry. We demonstrate that the method is converged with small grids containing <500 points/atom. We implement the algorithm on a GPU for increased efficiency and emonstrate the algorithm for molecules with up to a few dozen atoms. We explore the accuracy of the independent atom model (IAM) by comparison with our new and more accurate method. We also investigate the possibility of detecting signatures of electronic transitions in polyatomic pump–probe diffraction experiments.},
doi = {10.1021/acs.jctc.8b01051},
journal = {Journal of Chemical Theory and Computation},
number = 3,
volume = 15,
place = {United States},
year = {2019},
month = {1}
}

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This content will become publicly available on January 31, 2020
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