Chemistry Seminar with Professor Sharani Roy from University of Tennessee, Knoxville at 4:00pm
Bridging the pressure gap in theoretical models of gas-solid adsorption
Akin to the pressure gap between laboratory surface-science experiments performed under ultrahigh vacuum and industrial surface chemistry conducted under high gas pressures, theoretical models of gas-solid interfacial chemistry are often developed for low gas concentrations yet applied to surface phenomena that occur under high gas concentrations. The primary reason for this discrepancy is the steep cost of computing chemical properties at high surface concentrations (or coverages) of the gas using electronic structure methods. To address this challenge and to study the percolation of gases just beneath the surface, i.e., into the subsurface, at high coverages, we have developed lattice-gas adsorption models that include surface as well as subsurface sites in a crystalline solid and are fully parameterized using density functional theory (DFT). We have applied the models to study the adsorption of atomic oxygen on the Ag(111) surface, first as functions of coverage and temperature using canonical Monte Carlo simulations, and next as functions of pressure and temperature using grand-canonical Monte Carlo simulations. The simulations show the conditions under which subsurface adsorption occurs and provide insight into how subsurface adsorbates might participate in catalytic partial oxidation on silver surfaces. Overall, the lattice-gas adsorption model offers a simple and insightful theoretical framework to explore the competition between surface and subsurface adsorption in gas-surface systems.
Sharani received her BS degree in Chemistry from Hansraj College at the University of Delhi and her MS degree in Chemistry from the Indian Institute of Technology Delhi in India. During the latter, she simulated the melting of rare-gas clusters in the group of Dr. Charusita Chakravarty. Then she joined the Ph.D. program in Chemistry at Yale University, where she developed nonadiabatic gas-surface scattering simulations in the group of Dr. John Tully. After completing her Ph.D., she joined the group of Dr. Mark Ratner at Northwestern University as a postdoctoral research associate and modeled STM-induced molecular dissociation on metal surfaces and heterogeneous catalysis by metal-organic frameworks. At the University of Tennessee, her group develops theoretical models to understand chemistry at surfaces and interfaces at the fundamental level. Current research areas of interest include adsorption in the subsurface of metals, molecule-electrode interfacial effects on conductance in molecular junctions, and adsorption-induced proton transfer on surfaces. Sharani won the NSF CAREER award in 2018.