Research at CUC³

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 headings.

1. 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. J. Stone).

2. 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 (M. Sprik).

   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).

3. 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).

4. 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).

5. Biomolecular systems

   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).