Within the Born-Oppenheimer approximation the coupling between nuclear and electronic motion is neglected. This approximation is behind most ground state electronic structure methods for molecules and led to the development of efficient mixed quantum/classical schemes for performing ab initio molecular dynamics (AIMD), gives rise to considerable computational savings in comparison to the full quantum dynamics. However, as soon as more than one electronic state plays a role in the dynamics (for example for a photochemical reaction), the Born-Oppenheimer approximation will break down whenever the coupling between electronic states due to nuclear motion becomes important. Our group is interestingly in developing new theoretical and computational approaches for improving the rigorous description of coupled electronic and nuclear dynamics, while restricting the computational expense as much as possible! Developments are usually performed within the Quantics Quantum Dynamics Package, largely based around the Muti-Configurational Time-Dependent Hartree (MCTDH) and the Direct Dynamics Variational Multi-Configuraitonal Gaussian method.
A strong focus of the groups work in this area has been on developing model Hamiltonians to describe ultrafast dynamics. The aim of this work is to enable a uniformed description of excited state dynamics within a few dominant driving modes, in much the same way as an arrowing pushing mechanism in organic chemistry. This work is especially focused upon transitions metal complexes. These metal organic complexes are excellent model systems to study fundamental photophysical processes. After photoexitation, these molecular complexes may undergo any of a plethora of important phenomena including radiative (fluorescence and phosphorescence) decay, non-radiative intramolecular relaxation processes, such as internal conversion (IC) intersystem crossings (ISC, i.e. a spin change) and intramolecular vibrational redistribution (IVR). Most of these processes are accompanied or driven by structural changes occurring as the nuclei adapt to the new electronic structure. Besides this, transition metal complexes have also gathered significant attention owing to potential applications, such as photosensitisers in photovoltaics or photocatalysts. At the heart of such applications are the photoactive metal-to-ligand charge transfer (MLCT) states.
A strong focus of the groups work in this area has been on developing model Hamiltonians to describe ultrafast dynamics. The aim of this work is to enable a uniformed description of excited state dynamics within a few dominant driving modes, in much the same way as an arrowing pushing mechanism in organic chemistry. This work is especially focused upon transitions metal complexes. These metal organic complexes are excellent model systems to study fundamental photophysical processes. After photoexitation, these molecular complexes may undergo any of a plethora of important phenomena including radiative (fluorescence and phosphorescence) decay, non-radiative intramolecular relaxation processes, such as internal conversion (IC) intersystem crossings (ISC, i.e. a spin change) and intramolecular vibrational redistribution (IVR). Most of these processes are accompanied or driven by structural changes occurring as the nuclei adapt to the new electronic structure. Besides this, transition metal complexes have also gathered significant attention owing to potential applications, such as photosensitisers in photovoltaics or photocatalysts. At the heart of such applications are the photoactive metal-to-ligand charge transfer (MLCT) states.
This includes revealing the role of the solvent [paper1,paper2] and ultrafast intersystem crossing [paper3,paper4,paper5] in the photophysics of a prototypical Cu(I) complex (Figure above). These simulations have been used to predict the expected experimental signals of femtosecond X-ray spectroscopy. Related work on Fe(II) molecules [paper6,paper7,paper8] has revealed the close interplay between the electronic, spin and vibrational degrees of freedom, it is therefore crucial to understand these interactions and how they control the dynamics if one wishes to enhance the design of new molecular systems. Finally our work on an Au(I) complex has illustrated the connection between the intersystem crossing in metal systems and organic systems.
Our work in this area also includes method development. This is focused upon enhancing the ability of the simulations to more accurately capture the dominant processes experimentally. This includes acceleration on-the-fly simulations within the framework of the Direct Dynamics Variational Multi-Configuraitonal Gaussian method using Graphical Processing Unit. In addition we are especially interested in the role of the properties of laser field on the resulting dynamics [paper1,paper2,paper3].
Probing ultrafast non-equilibrium dynamics became possible with the advent of ultrafast time-resolved linear and non-linear optical spectroscopies. However, because optical spectroscopy consists of transitions between delocalised valence states, the link between the spectroscopic observable and structure is ambiguous for systems of more than one nuclear degree of freedom, i.e. >2 atoms. To overcome this, the last decades have witnessed a significant research effort aimed at exploiting short wavelength probe pulses to achieve direct structural sensitivity in time-resolved pump–probe experiments. The focus of this research effort is to develop the rigorous theoretical framework for simulating the experimental observables of time-resolved core-hole spectroscopy and diffraction experiments.
J. Phys. B 48:214001 (2015).
Phys. Chem. Chem. Phys. 17:23298-23302 (2015).
Structural Dynamics, 2:024302 (2015).
Coord. Chem. Rev. 277-278, 44-68 (2014).
Phys. Chem. Chem. Phys. 16:23157- 23163 (2014).
J. Phys. B 48:214001 (2015).
Phys. Chem. Chem. Phys. 17:23298-23302 (2015).
Structural Dynamics, 2:024302 (2015).
Coord. Chem. Rev. 277-278, 44-68 (2014).
Phys. Chem. Chem. Phys. 16:23157- 23163 (2014).