Simulations of vibrational spectra of nanoconfined solvents

(Thompson and Laird)

An undergraduate student in Dr. Thompson's group will use theoretical and computational methods to investigate infrared and Raman spectra in nanostructured silica pores. These spectroscopies are often used as experimental probes of the structure and dynamics of liquids in porous materials, e.g., supported catalysts, but the factors that determine the spectra in systems with nanoscale structure are not well established, complicating the interpretation. Mixed quantum-classical molecular dynamics (MD) and MD-based perturbation theory simulations will be used to obtain the spectra of neat liquids and dissolved solutes confined in model nanoscale silica pores. (Such simulations are suitable for undergraduates since the technical, e.g., coding, requirements can be adapted to each student's interest and/or ability; further, similar calculations have been mastered by a previous undergraduate in the group, David Ben Spry.) The Thompson group has already developed an approach for generating the silica pores with systematically controllable properties. Potential systems for study include liquid CH3I, CH3CN, and CH3OH as well as CN- and N3- solutes. The effects of pore size, surface chemistry, and solvent properties will be examined. Special attention will be paid to understanding the molecular mechanisms of spectral shifts and broadening (dephasing) in nanoscale confinement. In conjunction with these studies of vibrational dynamics, Dr. Thompson and Dr. Brian B. Laird (KU Chemistry) are collaborating on Gibbs-ensemble Monte Carlo simulations to determine the equilibrium liquid densities and structures in silica pores of varying size and surface chemistry.