The theoretical research and numerical modelling carried out at CUC3
cover an exceptionally broad range of topics in theoretical and
quantum chemistry, condensed matter science, surface science and
statistical mechanics of complex and disordered systems. Some of the
recent research is summarized below, conveniently listed under five
Quantum chemistry, intermolecular forces and spectroscopy
Cambridge has a long-standing tradition of excellence in
quantum chemistry and first principles calculations of intermolecular
forces. Presently the emphasis is on Kohn-Sham density functional
theory of the electronic structure and excited states of molecules.
The key problem is the development of accurate exchange and
correlation functionals of the electron density while accurate
information on excited states is gained from linear response theory
(N. C. Handy). Exact diagonalisation techniques are used to study
strongly-correlated electron quantum-dot systems (A. Alavi).
Another important application of quantum chemistry is the ab initio
determination of intermolecular potential energy surfaces, and the
development of analytical potential models that describe the
interactions to high accuracy, with applications to water, to
molecular clusters and to the adsorption of molecules on surfaces (A.
Ab initio simulations of condensed matter
Quantum density functional techniques for electronic
structure can be combined with Molecular Dynamics (MD) simulation
methods for the motion of the nuclei to explore condensed matter
systems involving hundreds of atoms and to study chemical processes
in the condensed phase (A. Alavi, M. Sprik).
One key problem is to relate the bands of extended electronic states
in condensed molecular systems to molecular orbitals of individual
molecules, which is of crucial importance, in particular, in
electrochemistry and electronic spectroscopy of solutions. Recent
methodological progress includes extensions of Car-Parrinello ab
initio MD to treat variable numbers of electrons, to implement
time-dependent DFT and to determine equilibrium constants in solution
Ab initio MD is also a powerful tool for the determination of
materials properties of solids and surfaces and is being applied to
transition metals, which are technologically important as
heterogeneous catalysts, and to charged surfaces held at a fixed
potential relative to a reference electrode, relevant for
electrochemical and interfacial processes (A. Alavi).
Energy landscapes of complex disordered systems
The study of energy landscapes (potential energy surfaces) of
many-body systems finds wide applications in Chemistry and Physics.
Thermodynamic and dynamic properties of complex systems can be
related to the underlying energy landscape by a proper sampling of
local minima and transition states that connect them, while global
optimization algorithms allow a determination of the lowest energy
state. Current work focuses on folding pathways for peptides,
aggregation of prions and the properties of 'strong' and 'fragile'
glass formers (J.P.K. Doye, D. J. Wales).
Complex fluids and soft matter
Complex fluids, including colloidal dispersions, polymer
solutions, and polyelectrolytes involve multiple length and time
scales, which require well controlled coarse-graining procedures
based on statistical mechanics and classical DFT of interfaces. A
systematic tracing out of microscopic degrees of freedom is being
used to derive state-dependent, effective interactions between
mesoscopic particles or proteins. Recent applications include studies
of colloid-polymer mixtures, of lamellar colloids (clays), of wetting
by ionic liquids, and of the dielectric behaviour of polar liquids
near interfaces. (J. P. Hansen, A.A. Louis).
Many of the theoretical and numerical techniques developed in
Theoretical Chemistry find a natural application to biomolecular
systems. Global optimization algorithms are being successfully
applied to predict tertiary protein structure from amino-acid
sequences, and to provide insight into prion structure (D. J. Wales).
The statistical methods developed for the study of complex fluids are
being extended to explore models for protein aggregation and
crystallization (A.A. Louis, J.P.K. Doye), and to ion channels
through membranes (J. P. Hansen). In the foreseeable future, ab
initio simulation techniques will provide new insight into the
coupling of electronic structure to the dynamics of biomolecules, in
particular electron transfer and redox reactions. (A. Alavi, M. Sprik).