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Summary: arXiv:0805.3803v2[quant-ph]15Aug2008
Coupling of electrons to the electromagnetic field in a localized basis
Roland E. Allen
Department of Physics, Texas A&M University, College Station, Texas 77843
A simple formula is obtained for coupling electrons in a complex system to the electromagnetic
field. It includes the effect of intra-atomic excitations and nuclear motion, and can be applied in, e.g.,
first-principles-based simulations of the coupled dynamics of electrons and nuclei in materials and
molecules responding to ultrashort laser pulses. Some additional aspects of nonadiabatic dynamical
simulations are also discussed, including the potential of "reduced Ehrenfest" simulations for treating
problems where standard Ehrenfest simulations will fail.
It is now possible to perform first-principles simu-
lations of the coupled dynamics of electrons and nu-
clei with all nuclear coordinates included [1, 2, 3, 4],
rather than a subset of nominal reaction coordinates.
For very large systems, or when many trajectories are
necessary, it is convenient to use a first-principles-based
scheme [5, 6, 7, 8], with a valence-electron Hamilto-
nian and ion-ion repulsive potential derived from calcu-
lations using density-functional or other first-principles
techniques. Here we are mainly concerned with the is-
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