One of the great successes in science over the last 50 years has been the application of quantum mechanics to the description of molecules and materials. The crucial step is describing the electrons in these systems, and so it is known as 'electronic structure theory', which is part of quantum chemistry, theoretical chemistry, condensed matter physics, electronic band structure theory or materials simulation.

Physical and chemical properties such as molecular structure, charge distributions, electronic spectra, vibrational spectra, polarisabilities, dipole moments and ionisation potentials can be readily computed for molecular scale systems or for extended solids using numerical methods and high performance computing.

Traditionally, the work horse of quantum chemistry was the Hartree-Fock approximation. In this approach, the many-electron wave function of atoms, molecules and solids is described using a self-consistent field (SCF) method. In an SCF calculation, an electron moves in the average field of all the other electrons in an atom, molecule or solid. In recent years, the density functional theory (DFT) has become an accurate and computationally efficient approach to the study of the electronic properties of matter. DFT calculations replace the calculation of a many-electron wave function with the direct calculation of the electronic charge density. DFT calculation of the charge density is computationally very similar to the SCF approach in wavefunction theory.

Extremely accurate calculation of electronic structure requires a 'correlated' treatment of the many-electron problem. Correlation allows electrons to avoid each other in ways that are described in SCF methods. Describing electron correlations is computationally very demanding and is usually restricted to small molecular systems. Methods useful for calculating electron correlations include configuration interaction, many-body perturbation theory (Moller-Plesset theory), and coupled cluster theory.

In the Electronics Theory Group, we apply the methods of quantum chemistry to explore materials science in relation to nanoelectronics and advanced technologies. We are investigating the role of electron correlations on molecular spectra and for molecular electronics.

Listed below are example publications from Electronic Theory Group members in the area of quantum chemistry and condensed matter physics.

1.Monte Carlo Configuration Interaction Predictions for the Electronic Spectra of Ne, CH2, C2, N2, and H2O Compared to Full Configuration Interaction Calculations, W. Győffry, R. J. Bartlett and J. C. Greer, Journal of Chemical Physics 129, 064103 (2008)

2.Electronic Current Density Expanded in Natural Orbitals, J. C. Greer, Molecular Physics 106, pp. 1363-1367 (2008)

3.Statistical Estimates of Electron Correlations, W. Győffry, T. M. Henderson and J. C. Greer, Journal of Chemical Physics, 125, 054104 (2006)

4.Quantum Mechanics at the Core of Multi-scale Simulations, R. J. Bartlett, J. McClellan, J. C. Greer, and S. Monaghan, Journal of Computer-Aided Materials Design, 13, pp. 89-109 (2006)

5.Determining Complex Absorbing Potentials from Electron Self Energies, T. M. Henderson, G. Fagas, E. Hyde, and J. C. Greer, Journal of Chemical Physics, 125, 244104 (2006)

6.Tools for Analysing Configuration Interaction Wavefunctions, P. Delaney and J. C. Greer, Computational Materials Science, 28 pp. 240-249 (2003)

7.A Basis Set Study for the Calculation of Atomic Excited States Using Monte Carlo Configuration Interaction, J. A. Larsson, L. Tong, T. Cheng, M. Nolan and J. C. Greer, Journal of Chemical Physics, 114 pp. 15-22 (2001)

8.Impact of Electron-Electron Cusp on Configuration Interaction Energies, D. Prendergast, M. Nolan, C. Filippi, S. Fahy, and J. C. Greer, Journal of Chemical Physics, 115 pp. 1626-1634 (2001)

9.A Monte Carlo Configuration Generation Computer Program for the Calculation of Electronic States of Atoms, Molecules and Quantum Dots, L. Tong, M. Nolan, T. Cheng and J. C. Greer, Computer Physics Communications, 131 pp. 142-163 (2000)

10.Electronic Correlation Energy in Linear and Cyclic Carbon Tetramers, J. C. Greer, Chemical Physics Letters, 306 pp. 197-201 (1999)

11.Monte Carlo Configuration Interaction, J. C. Greer, Journal of Computational Physics, 146 pp. 181-202 (1998)

12.A Parallelization Model for Successive Approximations to the Rayleigh-Ritz Linear Variational Problem, J.C. Greer, IEEE Transactions on Parallel and Distributed Systems, 9 pp. 938-951 (1998)

13.Alternative Equations of Motion for Dynamical Simulated Annealing of the Density Functional, J. C. Greer, Physical Review B, 53 pp. 10651-10655 (1996)

14.Estimating Full Configuration Interaction Limits from a Monte Carlo Selection of the Expansion Space, J.C. Greer, Journal of Chemical Physics, 103 pp. 1821-1828 (1995)

15.Consistent Treatment of Correlation Effects in Molecular Dissociation Studies Using Randomly Chosen Configurations, J. C. Greer, Journal of Chemical Physics, 103 pp. 7996-8003 (1995)

16.Structures and Spectra of Na(NH3)n=1,2, J. C. Greer, C. Hüglin, I. V. Hertel, and R. Ahlrichs, Zeitschrift für Physik D, 30 pp. 69-75 (1994)

17.Constrained Mechanics for the Dynamical Simulated Annealing of Coulomb Systems, J. C. Greer, Theoretica Chimica Acta, 88 pp. 363-373 (1994)

18.Proton Transfer in Ammonia Cluster Cations: Molecular Dynamics in a Self Consistent Field, J. C. Greer, R. Ahlrichs and I. V. Hertel, Zeitschrift für Physik D, 18 pp. 413-426 (1991)