A. Research Summary
The main focus of my research is the field of intermolecular interactions. I work on both the theoretical and computational aspects of this subject, and have made significant contributions to this field through the development of SAPT(DFT) (a symmetry-adapted perturbation theory based on density functional theory) and the Misquitta-Williams-Stone (WSM) method for molecular properties.
In brief, SAPT(DFT) (also known as DFT-SAPT) is an electronic structure method for calculation of intermolecular interaction energies that has a computational cost similar to MP2 but an accuracy close to CCSD(T) (one of the most advanced and accurate electronic structure methods that can be applied to moderately sized problems).
Additionally, the interaction energy from SAPT(DFT) is naturally split into physical components, such as the electrostatic, exchange, polarization and dispersion energies. This, combined with accurate distributed molecular properties from the WSM method, allow the construction of analytic potentials and provide a deep insight into the physical processes of molecular aggregation.
I work on the development and application of these methods. Currently my projects include:
- Potentials: Using SAPT(DFT) and the WSM methods to calculate very detailed intermolecular potentials. These include the effects of atomic anisotropy and polarizability.
- Organic Crystals: These potentials can then be used to predict the most stable structures of small ro meduim-sized organic molecules. Together with the group of Prof. Sally Price (UCL) and Prof Anthony Stone (Cambridge), I have been able to predict the crystal structure of C6Br2ClFH2 in the 2007 Blind Test of Crystal Structure Prediction organised by the CCDC. This was quite an achievement - the first for a completely ab initio method.
- Small-gap, extended systems: The interactions between extended (1 or 2-dimensional) systems with small HOMO-LUMO (band) gaps is qualitatively different from that between insulators. This was a significant result of some very recent work I have done with Ali Alavi, James Spencer and Anthony Stone. This has opened up a lot of possibilities as small-gap systems like carbon nanotubes and organic molecular wires are the basic components of a lot of work on nano-fabrication and nano-devices.
- Dispersion-corrected DFT: I am also currently working on very accurate dispersion corrections for DFT methods specifically applicable to water ice. My goal here is to achieve far higher accuracies than has been possible so far. The SAPT(DFT) and WSM methods are crucial here as I derive all parameters based on theory alone. This work, which is in it's final stages, can be readily extended to other systems.
- Soot: Soot particles are aggregates of polyaromatic
hydrocarbons (planar molecules of carbon and hydrogen atoms). Even at 2000K, the temperature in a petrol engine, the attractions between
such molecules can be strong enough to cause them to aggregate, forming elementary soot particles. In collaboration with Tim Totton, Markus Kraft (both in Chemical Engineering) and Dwaipayan Chakrabarti (Chemistry), I am trying to provide a detailed description of the structure and dynamics of these particles, and thence to understand the behaviour of reactant gases within them. This information, which cannot be obtained experimentally, is crucial for engine modelling, and could result in engines that produce little or no soot. There are important reasons why we need this: one is that smoke inhalation is the cause of many deaths (around 400,000 in India alone), and another is that soot is now thought to be second only to carbon dioxide in its effect on global warming, through its ability to absorb radiation in the upper atmosphere (Myhre, Science,2009).
Because soot has a lifetime of just a few days, improvements to combustion engines will have an almost immediate impact on global climate.
C. Selected Articles
A. J. Misquitta, J. Spencer, A. J. Stone and A. Alavi. Dispersion interactions between semi-conducting wires, Phys. Rev. B, 82, 075312-7 (2010).
A. J. Misquitta, G. W. A. Welch, A. J. Stone and S. L. Price. A first principles prediction of the crystal structure of C6Br2ClFH2, Chem. Phys. Lett. 456, 105(2008).
A. J. Stone and A. J. Misquitta. Atom-atom potentials from ab initio calculations, Int. Rev. Phys. Chem. 26, 193(2007).
A. J. Misquitta, B. Jeziorski, and K. Szalewicz. Dispersion energy from density-functional theory description of monomers, Phys. Rev. Lett. 91, 033201(2003).
A. J. Misquitta and K. Szalewicz. Intermolecular forces from asymptotically corrected density functional description of monomers, Chem. Phys. Lett. 357, 301(2002).
CamCASP is a collection of scripts and programs for the calculation ab initio of distributed multipoles, polarizabilities, dispersion coefficients and repulsion parameters for individual molecules, and interaction energies between pairs of molecules using SAPT(DFT). Authors: A. J. Misquitta and A. J. Stone. Web site: http://www-stone.ch.cam.ac.uk/
SAPT2008: An Ab Initio Program for Many-Body Symmetry-Adapted Perturbation Theory Calculations of Intermolecular Interaction Energies. Web site: http://www.physics.udel.edu/ szalewic/SAPT.
This is not an exhaustive list and I would be happy to discuss other project possibilities.
|A new generation of interaction models|
|Ab initio methods for electronic charge-transfer|
|Interaction energy models based on the denstiy|