In the Willard group we use theory and simulation to explore the role of molecular fluctuation in a variety of chemical phenomena. We are particularly interested in systems for which a mean field approach, i.e., the averaging out of molecular-level detail, fails to reproduce experimental results. This is often a consequence of complex molecular scale behavior such as collectivity, spatial or dynamic heterogeneity, or the coupling of fast and slow time or length scales, which can give rise to interesting and unexpected macroscopic phenomena.
One area we investigate involves the dynamics of excited electrons in conjugated molecular systems. Electronic properties such as potential energy and spatial distribution are highly sensitive to the configuration of the molecule(s) on which an electron resides. A manifestation of this sensitivity is that the properties of organic electronic devices (bulk-heterojunction type solar cells for example) often depend significantly on the molecular morphology of the active material. An improved understanding of the relationship between molecular morphology and the static and dynamic properties of excitons, i.e., Coulobmically bound electron-hole pairs, is needed in order to guide the design of future generations these materials. Our approach involves combining methods of statistical mechanics with quantum dynamics in order to elucidate the interplay between molecular disorder and exciton dynamics.
Another research area of interest to our group is the study of liquid water interfaces. In particular we investigate the intrinsic molecular structure of the water-substrate interface and how that structure is influenced by the shape or surface chemistry of the substrate. Typically the interface between liquid water and a substrate (e.g. protein surface, cell membrane, polymer surface…) is made rough by fluctuating substrate topography or through capillary wave type thermal fluctuations in the position of the interface. In the context of molecular simulation it is possible to adopt a frame of reference that removes these spatial undulations, retaining only those intrinsic molecular feature of the liquid phase boundary. By doing so we seek to uncover the influence of substrate chemistry on the molecular structure of the intrinsic interface and determine what role, if any, such an influence plays in a variety of interface-mediated chemical processes.