Excited State Specific Correlation Methods in Quantum Chemistry

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

With support from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry, Eric Neuscamman of the University of California at Berkeley is developing new tools for the computer simulation of light-driven chemistry. Whether studying DNA damage from sunlight or industrial processes that mimic photosynthesis, understanding the mechanisms by which light drives chemical change is made difficult by the tiny scales and fast pace at which the action occurs. Modern experimental techniques can offer glimpses of what is going on, but often leave key questions unanswered, such as the full series of shapes a molecule transforms itself through after absorbing energy from sunlight. The Neuscamman group will develop and deploy a new generation of computer models that faithfully simulate these processes in high priority areas of chemistry where current methods are limited. In particular, light-driven processes that move electrons from one side of a molecule to the other or that move multiple electrons at once cannot be simulated accurately by current tools except in the smallest molecules, whereas key applications of these processes occur in technological and biological settings involving hundreds of atoms. By bridging this gap, the Neuscamman group aims to deepen our understanding of light-driven chemistry and the crucial technologies that rely on it. In tandem with this research, the Neuscamman group will expand its outreach work to middle school students, teaching the underlying principles of mathematical optimization methods that support scientific priorities from chemistry to machine learning. This game-based outreach will also plant seeds around concepts like slope and curvature so that students are already familiar with exciting and lucrative real-world uses for calculus when they eventually find themselves in a calculus classroom. By engaging undergraduate students as instructors in this outreach, the activity will both broaden middle school student horizons and reinforce understanding for the active undergraduate co-worker participants. Understanding the energies of transitions in which molecules absorb light is central to chemistry. While decades of theoretical work have been dedicated to predicting the transition energies of electronic (e.g. HOMO→LUMO) excitations in particular, some categories of electronic excitation are still poorly served by available theoretical methods. Two examples of these are charge transfer states, which are central to biological and artificial light harvesting as well as many enzymatic reaction mechanisms, and double excitations, which are common in the extended π-conjugation networks of pigments and chromophores as well as in many transition metal complexes. The Neuscamman group will build on recent breakthroughs in the mean-field treatment of electronically excited states to construct what is anticipated to be a highly accurate, and affordable suite of coupled cluster and related methods for modeling electronically excited states in large molecules and molecular assemblies. These methods have the potential to significantly improve the state-of-the art in modeling both charge transfer and doubly excited states with potential broad long term scientific impacts for chemistry, biology, materials and systems chemistry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.