Theory, Computation and Simulation
Reseach Theme Leader: Professor Paul Popelier
Researchers
Chemical theory and computation provides important insights into, and predictions for, chemical systems ranging from small gas phase molecules to large biological molecules having thousands of atoms. This has been achieved through a combination of fundamental theories using both quantum and statistical mechanics. When coupled with modern computational techniques, these theories can be applied to large and complex systems. Computational chemistry is now recognised as an important discipline within chemistry. It impinges not only on the three traditional areas but also makes important contributions in interdisciplinary areas such as life science and materials science. The group at Manchester is at the forefront of developing new methods and applying them to current chemical problems. In particular:
- J McDouall: The proper description of metal containing systems remains a challenge for quantum chemistry. In particular, the accurate prediction of spectroscopic parameters and the role of relativistic effects on these are still in their infancy. Active and funded areas of work include: developing an understanding of the factors that govern zero field splittings in systems containing first row transition metals and their significance in determining the properties of magnetic molecules; the prediction of the electronic structure and EPR properties of molybdenum and tungsten containing systems, which may serve as templates for the design of molecular wires; the extension of such studies to predict the spectroscopy of lanthanide and actinide containing systems. The work involves a mixture of the use of established computational methods and the development of new strategies and methods. A close collaboration with experimental groups focuses the relevance of the work.
- P O’Malley: Computational methods based principally on Density Functional Theory (DFT) are used to model the structure and spectroscopic properties of bioinorganic complexes DFT procedures for the accurate calculation of a wide range of spectroscopic parameters are developed, including EPR hyperfine couplings, g-values and zero-field splitting parameters as well as quadrupole couplings and chemical shifts obtained using Mossbauer spectroscopy. Methods based on Quantum Mechanics/Molecular Mechanics (QM/MM) are also developed to model active sites in proteins. In particular, transition metal complexes and prosthetic groups involved in photosynthetic electron transfer are investigated with a view to obtaining a better understanding of electron transfer mechanism and also to provide design features for artificial solar energy converters.
- R Henchman: Liquids and solutions are fundamental components of many chemical systems. However, the theories to predict and explain their thermodynamic and kinetic properties are insufficient to explain many important phenomena, even for the supposedly simple system of liquid water. Henchman is developing an approach to address this need based on quantities derived from the ensemble of structures generated in a computer simulation of the system.
- J Connor: Chemistry in the gas phase is the result of collisions between atoms and molecules, and it is essential to understand in detail how one atom or molecule collides with a second atom or molecule. New and powerful theoretical methods are being developed to describe and predict state-of-the art experimental results for elastic, inelastic and reactive collisions.
- N Burton: In the exploration of structures and transition states of biochemical reactions, hybrid quantum mechanical and molecular mechanical (QM/MM) methods can be combined with direct dynamics calculations to obtain accurate reaction profiles for the proton transfer step of enzyme reactions, including insight into tunnelling. In the area of physical organic chemistry, proton transfer reactions in intramolecular complexes can be studied as mimics for enzyme reactions. Transition path sampling enables the study of the conformational free-energy landscape and rates of molecular conformational change in flexible carbohydrates. Electronic structures, particularly of transition metal complexes can be difficult to understand resulting in complex and varied reactions. Magnetic properties, such as NMR shielding, are useful indicators of electron density distributions in molecules and magnetically induced currents can be a useful indicator of electron delocalisation and bonding. Finally, research of actinide chemistry focuses on the speciation and interaction of important complexes, which are relevant to the nuclear industry, with common minerals such as calcite.
- P Popelier: A fundamental theory called Quantum Chemical Topology (QCT) proposes a definition of two cornerstones of chemistry: atoms and bonds, directly computable from contemporary wave functions. Both can be represented numerically as well pictorially. Further chemical insight, such as electron pair localisation, bond order, aromaticity and electronegativity can be obtained from QCT. As a modern way to compute molecular fragments, QCT was used to set up the Quantum Isostere Database (QID), which serves as a bioisoteric replacement tool in the design of drugs and agrochemicals. As a rigorous instrument to gauge atomic transferability, QCT is also the basis of the construction of a novel force field. Atoms are described by multipole moments rather than point charges, which is essential for accurate short-range electrostatics. Polarisation is captured by machine learning, again enhancing the realism of the QCT force field. Furthermore, QCT provides new descriptors, directly harvested from wave functions, which were proven to be successful in a wide variety of validated medicinal, ecological and physical organic quantitative structure activity relationships. pKa prediction from simple quantum chemical calculations is currently a priority.
In the area of materials science there is strong collaboration with the Organic Materials Innovation Centre (OMIC), also in the School of Chemistry, focusing in particular on electro-optical devices. In the area of life science there is strong interaction with the Manchester Interdisciplinary Biocentre (MIB).
