Collaborative Research: Theoretical description of electron-driven chemical processes and related reactions

Purdue University, West Lafayette IN

Investigators

Abstract

WIth support from the Chemical Theory, Models and Computational Methods (CTMC) Program in the Division of Chemistry, Chris Greene of Purdue University and Viatcheslav Kokoouline of the University of Central Florida (UCF) will collaboratively work to solve a class of quantum mechanical problems related to electron collisions with molecules having physical or biochemical relevance. When a low energy electron strikes a molecule, several possible outcomes can occur, including bond breakage leading to fragmentation into smaller molecules and atoms. This class of physico-chemical processes has proven to be extremely challenging for current theoretical methods to describe. To overcome current limitations of theory, Greene and Kokoouline will apply a mathematical and computational set of tools to determine the rate at which such bond-breaking reactions occur. The need to understand these electron-initiated chemical processes resonates across several disparate fields, including chemical astrophysics, plasma chemistry, and radiation biochemistry. A deeper understanding of the sequence of events that is triggered when a slow electron impacts DNA (2'-deoxyribonucleic acid) will help to understand how single or double strand breaks occur. While the principles of quantum mechanics are understood generally, applications of those principles to treat theoretical problems of this complexity and to compute collision outcomes accurately are extremely difficult and the field will benefit from the improvements to be developed by this project. An educational broader impact derives from the training of students, both graduate and undergraduate, as well as postdoctoral scholars, engendering them with the computational and theoretical tools needed to tackle difficult problems in this subfield. This collaborative research effort by Drs. Chris Greene and Viatcheslav Kokoouline of Purdue University and UCF, respectively, will concentrate on a select set of target molecular systems, selected to serve as prototypes of these non-perturbative chemical processes in which energy is converted from electronic into dissociative degrees of freedom. The research proposed here aims to improve theoretical capabilities for treating problems in physical chemistry that go beyond the usual paradigm of the field, which is the Born-Oppenheimer approximation. The normal rubric of the field treats any reactive process initially by computing one electronic potential surface, or in some cases a few such surfaces with couplings, as a function of the nuclear coordinates, followed by solution of coupled differential or partial differential equations relating to motion on those surfaces in either time-dependent or time-independent quantum mechanics. While this rubric has yielded many successes in treating reactive chemical and photochemical processes, electron-driven chemical transformations continue to pose severe challenges to existing theory. Therefore the Greene/Kokoouline team will endeavor to advance current theoretical approaches in two largely separate directions. Firstly, the electronic calculation will be developed with explorations of three-dimensional finite-element calculations with effective electron-molecule interaction potentials modeled with correlations approximately included through the introduction of static potentials that incorporate density-functional theory potentials. Secondly, the computational methods will be significantly improved to enable calculations of the bond-breaking that occurs in large molecules, especially those having biological relevance. In an outreach activity supported by the UCF team, Viatcheslav Kokoouline will also develop a web-based platform and a related methodology to teach quantum mechanics in studio-mode like classes that will then be made available to the community. 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.