Applications are invited for a postdoctoral research associate position in computational chemistry at Loughborough University. This is a DSTL funded position to work with Dr Kenny Jolley and Dr Felix Plasser (Chemistry, Loughborough University) on predicting the crystal structure, dynamics and physical properties of energetic materials.
The successful applicant will conduct molecular dynamics (MD) and accelerated MD simulations on energetic compounds. Bulk physical properties, stability to shock and heat, and reaction pathways will be modelled and compared to experimental data. In a later stage, we will perform time-resolved simulations of explosion processes.
This position is ideally suited for an ambitious early career researcher with a background in computational chemistry and materials modelling. The successful candidate will be highly motivated with a strong research track record and a desire to pursue multidisciplinary research.
The paper deals with the fact that the widely used CASSCF method, if not used carefully, can yield large errors (1-2 eV) in vertical excitation energies. This problem arises for ionic states, as defined within valence bond theory. Within this work we developed a simple diagnostic to identify ionic states. We found a good correlation between the new diagnostic (Qta) and the error, as shown in the figure above.
We hope that the new diagnostic will be useful similar to analogous diagnostics identifying charge transfer states in TDDFT computations. This will give users the possibility to spot potential problems quickly.
On-going work is concerned with going from just diagnosing the problem to developing a numerical correction term to fix the problem.
The singlet HOMO/LUMO transition (S2, 1La) is shown to be strongly aromatic whereas the triplet HOMO/LUMO transition (T1, 3La) is antiaromatic. Does this mean states reached by the same kind of orbital transition behave differently depending on their spin-multiplicity?
The aromatic S2 lies above the antiaromatic S1 even though S2 is the HOMO/LUMO transition. Does this mean that singlet antiaromaticity is actually a stabilising effect?
We have discussed the excited states of naphthalene from an entirely different viewpoint in a recent J. Chem. Theory Comput. article. It would be fascinating to combine the two viewpoints.
We just posted a preprint discussing a question I have been wondering about for a while: Why is the lowest excited state of a molecule not always the HOMO/LUMO transition? More generally we show how singlet and triplet state energies are affected in different ways by post-MO energy terms.
The topic of doubly excited states has been discussed quite controversially in the literature over the last couple of years, see for example JACS, 139, 13770 (2017) and JCTC14, 9 (2018), and it is often disputed whether to classify a state as doubly excited at all. To contribute to this discussion we worked on the development of a physically motivated definition of doubly excited character based on operator expectation values and density matrices, which works independently of the underlying orbital representation. We hope that this approach will provide new understanding on these issues.
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