Theoretical studies of small molecules
and of molecular processes
Concepts taken from electronic structure theory have been of immense
importance in the historical development of chemistry, and continue to
play a key role in the modern understanding of molecular electronic
structure and reactivity. Such concepts not only allow us to rationalize but
also to make predictions for whole classes of new systems.
Much of our research work involves the development and applications
of modern valence bond approaches to electronic structure – especially
the spin-coupled (SC) approach, which provides a simple highly visual model
of the behaviour of correlated electrons in molecules, whilst also producing
results of high accuracy. Applications include:
Studies of organic reaction pathways, typically for electrocyclic
reactions. For example, we examined SN2 identity
reactions, addition reactions of singlet dihalocarbenes, aromatic versus
diradical character in Cope rearrangements, and hetero-Diels-Alder reactions.
More recently we investigated homoaromaticity and
polycyclic fused aromatic compounds involving cyclopropenyl rings.
Main collaborator: Peter Karadakov at the
University of York. See, especially, here for
some nice pictures and explanations.
Developing and applying new 'auxiliary' tools for analyzing the
wavefunctions, electron densities and density matrices from high-level
calculations (typically using SC and CASSCF calculations as a testing ground).
Most recently we have been using domain-averaged Fermi hole (DAFH) analysis
and various multicentre bond indices to understand the bonding in a range of
systems, including recently-characterised formally Be(0) complexes.
We use various computational strategies, including the
CASVB algorithms that have been released for
general use via MOLPRO and also via
The most recent version is included in MOLPRO2015.1.
CASVB can be used either
to perform fully-variational optimization of fairly general types
of (multiconfigurational) modern VB wavefunctions or
to generate representations of CASSCF wavefunctions in modern VB form,
using overlap-based (relatively inexpensive) or energy-based criteria.
Other research interests
Charge-transfer processes in astrophysical environments
Properties of fluids under pressure
QSAR and momentum-space concepts
Sizing of gold nanoparticles by differential centrifugal sedimentation