Our collaboration with Tom Markland's group at Stanford University is published in J. Chem. Phys.

Unraveling electronic absorption spectra using nuclear quantum effects: Photoactive yellow protein and green fluorescent protein chromophores in water
In this manuscript, we use ab initio molecular dynamics, ab initio path integral molecular dynamics, and our recently introduced ensemble plus zero-temperature Franck-Condon (E-ZTFC) approach to simulate the optical absorption spectra for two systems that have posed a challenge to theory: the PYP and GFP anionic chromophores in water.  We show that using the E-ZTFC approach with sampling of nuclear configurations with ab initio path integral molecular dynamics leads to a significant improvement in simulated spectral widths and shapes compared to the standard ensemble approach with sampling configurations from ab initio molecular dynamics.

For these systems with strong chromophore-solvent interactions, we systematically characterize the contributions to the spectra due to nuclear quantum effects, direct and indirect interactions of the chromophore with solvent, and vibronic transitions, quantifying the spectral broadening with each contribution. We find that nuclear quantum effects broaden the spectra in three ways: through a larger spread of vertical excitation energies due to the larger distribution of C-C and C-N bond lengths in the chromophores, through a larger spread of vertical excitation energies due to direct chromophore-solvent interactions (where we find this to be a collective solvent effect rather than due to specific hydrogen bond interactions), and through the redistribution of spectral weight in the vibronic shape function. Although recent work has identified this first source of spectral broadening due to nuclear quantum effects, the latter two mechanisms are first identified here.