The Bearpark Group

We develop computational chemistry methods for excited states of large molecules. We also apply these methods in collaboration with experimental research groups, or to problems suggested by experiment.

Both of the computational methods we currently develop are hybrid quantum mechanics/molecular mechanics (QM/MM) methods:

MMVB
ONIOM

Each involves identifying part of a molecule that needs to be calculated more accurately than the remainder: for example, a chromophore which changes geometry in an excited electronic state.

One of the most important early applications of the MMVB method was in explaining the anomalous fluorescence of the azulene molecule. This depends on an accessible crossing between potential energy surfaces (conical intersection) between the ground (S₀) and first excited (S₁) states, leading to rapid radiationless decay, and the lack of such a crossing between first and second (S₂) excited states.

Subsequently, the same type of crossing has been shown to occur in other molecules, particularly fulvene. Here, several distinct points on a seam of S₁/S₀ intersection can be identified, similar to the way minima and transition structures can be identified on a single potential energy surface. This - together with the connection between the twisted S₁/S₀ crossings in fulvene and the Jahn Teller crossing in the cyclopentadienyl radical (PCCP)- has led to methods for investigating extended regions of electronic state degeneracy.

For a recent review which describes how excited state calculations can be carried out and used to investigate photophysical and photochemical decay processes see:

"Computational Investigation of Photochemical Reaction Mechanisms"
L. Blancafort, F. Ogliaro, M. Olivucci, M. A. Robb, M. J. Bearpark, A. Sinicropi, pp. 31-110 in Computational Methods in Photochemistry, ed. A. Kutateladze, CRC Press, Boca Raton (2005).

Research Highlights:

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