Accurate Nonadiabatic Dynamics at Conical Intersections in Nanomaterials

Michigan State University, East Lansing MI

Investigators

Abstract

In this project funded by the Chemical Theory, Models, and Computational Methods program, Professor Benjamin G. Levine of Michigan State University is developing new computational methods to model non-radiative recombination in semiconductor nanomaterials. Non-radiative recombination is a fundamental process that converts electronic energy to heat, thus limiting the efficiencies of devices for solar energy conversion, light emission, and other applications. The methods being developed provide an atom-by-atom, electron-by-electron mechanistic picture of this process, thus informing the design of future materials. Specifically, the Levine group is applying these new theoretical models to elucidate the dynamics of electronically excited silicon nanoparticles, which show promise as light emitters for solid state displays, biological imaging, and solid state lasers. The Levine group is also working with local high school teachers to develop the High School Computational Chemistry Server (HiSoCCS), which freely serves research-grade computational chemistry capability via a user-friendly web-based interface. HiSoCCS and associated curricular materials are made available for free to Michigan high schools. The Levine group's approach is based on the hypothesis that conical intersections, points of degeneracy between electronic states, are introduced by defects in the material, and that these intersections provide efficient pathways for non-radiative recombination. A new fully quantum mechanical method for modeling dynamics near conical intersections, the diabatized Gaussians on adiabatic surfaces (DGAS) approximation, is being developed. The DGAS wave function ansatz is designed to handle singularities in the first- and second-derivative nonadiabatic couplings that occur at conical intersections. The DGAS method is being implemented for high performance parallel computers, and the resulting software will be made freely available to other scientists. The broader impacts of this work include: a) the development of a new nonadiabatic molecular dynamics method capable of accurately modeling a wide range non-radiative processes, b) new open source software for modeling dynamics near conical intersections, c) a deeper understanding of non-radiative recombination in silicon nanomaterials, and d) new tools and materials that incorporate research grade calculations into the high school science curriculum.