Paul A. Johnson
Université Laval
Mean-field for strong electron correlation
Weakly-correlated systems are well-described as individual electrons. The dominant contribution to the wavefunction is a Slater determinant of the occupied orbitals, with small corrections provided by others with occupieds swapped for virtuals. For strongly-correlated systems this is not the case. Many Slater determinants contribute substantially and thus the correct physical picture is not independent electrons. To better understand these types of systems we are working with exactly solvable models which describe the correct first-order behaviour. Specifically, we employ their eigenvectors as a basis in which to write the physical wavefunction. Results will be presented for molecular dissociations.
Sasannah Bourne-Worster
University of Bristol
Unravelling the mechanism of concentration quenching
Chlorophyll molecules in photosynthetic light-harvesting complexes are surprisingly immune to the rapid fluorescence quenching displayed by solvated chromophores at high concentrations. The effect has consequently not been given much attention in studies of natural light-harvesting [1]. However, its impact cannot be further overlooked in the context of biomimetic antennae, since protection against this unproductive quenching pathway must necessarily be a critical design consideration.
We aim to provide concrete theoretical evidence to support of refute the leading hypothesis for the mechanism of concentration quenching: fast internal conversion to the ground state via a low-lying charge transfer state [1,2]. Making use of newly emerging fast methods in quantum chemistry [3], we extract Marcus potential energy surfaces from molecular dynamics simulations of solvated chromophores. These surfaces can be used to calculate the rates of transfer between the ground, excited and hypothesised charge-transfer states, to understand the overall quenching rate for a given chromophore concentration. By comparing these calculated rates to published experimental data [4,5], we aim not only to assess the feasibility of the proposed quenching mechanism, but also to understand the role of the photosynthetic protein environment in preventing it.
[1] Seely, G. R. Photochem. Photobiol. 27, 639–654 (1978)
[2] Krüger, T. P. J. et al. J. Phys. B At. Mol. Opt. Phys. 50, 132001 (2017)
[3] Grimme, S. et al. J. Chem. Theory Comput. 13, 1989–2009 (2017)
[4] Watson, W. F. et al. J. Chem. Phys. 18, 802–809 (1950)
[5] Beddard, G. S. et al. Nature 260, 366–367 (1976)