From semiconductor etching to molecular memories, from fuel cells to photosynthesis, much essential chemistry is driven by the collective motion of excited electrons (Figure 3.1). Yet computing the dynamics of strongly coupled, nonadiabatic, condensed system electrons on a large scale remains a challenge to theory. We have developed a method called the electron force field, which in conjunction with another method called wave packet molecular dynamics, makes simulations of these systems practical.
In wave packet molecular dynamics [5,16,3], nuclei are propagated as classical particles, and electrons as localized wave packets described by their average position and size.
In the electron force field (eFF), energies and forces are calculated from an energy expression parameterized as a function of nuclear and electron coordinates, with terms that capture key chemical features like covalent and ionic bonding, core-valence separation, lone pairs, correlation, and the mixing of metallic electrons. Details of the energy expression, as well as an analogy to classical force fields, are given in more depth below.
With our method, we expect simulations of excited electrons over picoseconds to be practical for a wide range of strongly coupled condensed systems.