Theoretical modelling
Starting from an atomic-level description, the aim is to provide interpretations of experimental results, to predict new results, as well as to propose new ideas for observing and controlling the transformation of matter at the atomic scale. The methods comprise of analytic theory and model development in combination with computational work in the effort to:
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Determine the molecular potential energy surfaces relevant for the nuclear dynamics.
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Map out the nuclear dynamics on these potential energy surfaces.
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Calculate experimental observables (signals) from the nuclear dynamics.
Quantum
chemistry ab initio
calculations are used to characterize potential energy surfaces. Of
particular importance to us are the properties of electronically
excited states along the degrees of freedom that are involved in a
given transformation. These studies can reveal topological features
such as conical intersections and avoided crossings – their nature
is of outmost importance for the interpretation of pump-probe
experiments. We employ complete active space (CAS) and time-dependent
density functional theory (TD-DFT) methods. These methodologies are
implemented in a variety of packages – we are experienced users of
the Gaussian03 and Molpro subset [67 Gaussian 03
(Revision A.1), M.J. Frisch, et al. (Gaussian, Inc.,
Pittsburgh PA, 2003). MOLPRO (version 2002.6), H.-J. Werner, et al.
(Birmingham, UK, 2003); http://www.molpro.net
].
Another approach to modelling is Molecular Dynamics, where the standard newtonian equations of motions are solved for large ensembles of molecules. This is a tiered approach, where first the charge distributions and mechanical properties of the relevant molecules are calculated through the methods introduced above, after which a simulation is set up and allowed to evolve according to newtonian dynamics.
