Size dependent errors in density-functional theory

Our recent studies into the errors in the excitation energies and ionization potentials as computed with density-functional theory (DFT) show size-dependent trends. This can be related to the delocalization error of standard density functionals; we are investigating how the inclusion of exact exchange into the functional affects these size-dependent errors

Determining accurate solvation models

The solvation environment around a solute has a large influence on molecular properties, but the extent of long-range solvation effects is unclear. It is thus not known how much solvent needs to be included to compute converged properties. We aim to (1) determine the amount of QM solvent necessary to compute converged solute properties in MM and PCM environments and (2) establish QM, QM/MM, and MM methods for accurate sampling of solute-solvent interactions in molecular dynamics. 

Modeling the absorption spectra of coupled chromophores

We want to move beyond understanding chromophore optical properties at the single molecule level and also understand them when they are coupled together in a thin film material. Absorption spectra are often quite different in dilute solution than in the aggregate, and our research aims to relate the configuration of multiple chromophores to the shifting and broadening of the computed and measured absorption spectra.

Real-time electron dynamics with time-dependent density-functional theory

Electronic charge transfer is key to harnessing photon derived energy.  After photo-excitation, the excited electrons must be transferred between phases, materials, or molecules. Thus, developing and benchmarking a method to directly model these electron dynamics is key to understanding these charge transfer processes at a fundamental level. Real-time TDDFT is a promising technique wherein the electron density matrix is explicitly propagated in time. This technique goes beyond the standard perturbative linear response TDDFT method, allowing the electron dynamics to respond to large perturbations such as an applied laser field. We use, develop, and validate this coherent superposition single-determinant density propagation method, examining the validity of the adiabatic approximation in the realm of strong-field perturbation of the electron density.