Professor Malcolm Heggie
Professor of Physical and Computational Chemistry
Email: m.heggie@surrey.ac.uk
Phone: Work: 01483 68 3541
Room no: 16 AZ 03
Further information
Research Interests
Analysing and predicting the behaviour of materials of technological and geological importance with first principles modelling.
'From first principles' is the proudest claim of theory - effectively it means we do not need experimental input. The tremendous advances in computer hardware and software mean that this approach is now feasible. It can be applied generally, but most importantly for problems which are intractable experimentally, like understanding the behaviour of materials in extreme environments like inside a nuclear reactor or a planetary interior.
The strength of the first principles approach is its independence. Two methods, experiment and theory, which arrive at the same answer independently provide convincing proof that a given result is right. In practice, theory always has to be informed at some level by experiment, because the number of theoretically possible options that would need to be tested otherwise would tend to the infinite.
Experiment also is the final arbiter of correctness. As Richard Feynman said:
“In general we look for a new law by the following process: first we guess it. Then we compute the consequences of the guess to see what if this is right. If this law that we guessed is right we see what it would imply and then we compare those computation results to nature. If it disagrees with experiment it’s wrong. In that simple statement is the key to science. It doesn’t make any difference how beautiful your guess is. It doesn’t make any difference how smart you are, who made the guess or what his name is. If it disagrees with experiment it’s wrong that’s all there is to it”
In studying radiation damage in graphite we came to the conclusion that the historic model of atomic displacement was not the only way that the crystal responds, but rather the graphite layers (graphenes) must buckle and fold as well. Our model invokes a key role for basal slip in graphite. We are currently computing the consequences of this 'guess' to see whether it is right and leading a consortium of experimental and theoretical research teams in Huddersfield, Leeds, Manchester, Nottingham and Salford to prove or falsify the theory.
Radiation damage in graphite is not only a field of demonstrable social and economic impact, but it is a field rich in concepts for graphene and carbon nanotube research, which also forms part of our portfolio.
Publications
Journal articles
- . (2012) 'Electron microscopy of nuclear graphite: A modelling approach'. Journal of Physics: Conference Series, 371
- . (2011) 'Muonium chemistry and spin dynamics in sulphur, modelling interstitial hydrogen.'. J Phys Condens Matter, England: 23 (31)
- . (2011) 'Low-energy termination of graphene edges via the formation of narrow nanotubes.'. Phys Rev Lett, United States: 107 (6)
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(2011) 'Low energy graphene edge termination via small diameter nanotube formation'. American Physical Society Physical Review Letters, 107 (6)Full text is available at: http://epubs.surrey.ac.uk/745280/
Abstract
We demonstrate that free graphene sheet edges can curl back on themselves,reconstructing as nanotubes. This results in lower formation energies than any other non-functionalised edge structure reported to date in the literature. We determine the critical tube size and formation barrier and compare with density functional simulations of other edge terminations including a new reconstructed Klein edge. Simulated high resolution electron microscopy images show why such rolled edges may be difficult to detect. Rolled zigzag edges serve as metallic conduction channels, separated from the neighbouring bulk graphene by a chain of insulating sp$^3$-carbon atoms, and introduce Van Hove singularities into the graphene density of states.
- . (2011) 'Buckle, ruck and tuck: A proposed new model for the response of graphite to neutron irradiation'. Journal of Nuclear Materials, 413 (3), pp. 150-155.
- . (2011) 'Journal of Physics: Conference Series: Preface'. Journal of Physics: Conference Series, 281 (1)
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(2010) 'Comment on "increase in specific heat and possible hindered rotation of interstitial C2 molecules in neutron-irradiated graphite"'. Physical Review B - Condensed Matter and Materials Physics, 82 (5)Full text is available at: http://epubs.surrey.ac.uk/741005/
Abstract
Iwata and Watanabe's model for the observed low-temperature specific heat of neutron-irradiated graphite assumes that self-interstitial atoms exist as clusters of nearly free C2 molecules. We suggest that their hypothesis is not supported by other experiments and theory, including our own calculations. Not only is it inconsistent with the long-known kinetics of interstitial prismatic dislocation loop formation, density-functional theory shows that the di-interstitial is covalently bonded to the host crystal. In such calculations no prior assumptions are made about the nature of the bonding, covalent or otherwise. © 2010 The American Physical Society.
- . (2008) 'The di-interstitial in graphite'. Journal of Physics Condensed Matter, 20 (39)
- . (2007) 'Anomaly enhancement of the dislocation velocity in SiC'. Physica B: Condensed Matter, 401-402, pp. 62-66.
- . (2007) 'Radiation defects in graphite'. Philosophical Magazine, 87 (31), pp. 4797-4846.
- . (2007) 'Density functional calculations on the intricacies of Moiré patterns on graphite'. Physical Review B - Condensed Matter and Materials Physics, 75 (23)
- . (2007) 'Electrical activity and migration of 90° partial dislocations in SiC'. New Journal of Physics, 9
- . (2007) 'First-principles simulations of boron diffusion in graphite.'. Phys Rev Lett, United States: 98 (1)
- . (2007) 'Partial dislocations under forward bias in SiC'. Materials Science Forum, 556-557, pp. 279-282.
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(2007) 'Core structures and kink migrations of partial dislocations in 4H-SiC'. Faraday Discussions, 134, pp. 353-367.doi: 10.1039/b603920k
- . (2007) 'Structure and energy of partial dislocations in wurtzite-GaN'. Physica Status Solidi (C) Current Topics in Solid State Physics, 4 (8), pp. 2945-2949.
- . (2007) 'Dislocations of Burgers vector c/2 in graphite'. Physica Status Solidi (C) Current Topics in Solid State Physics, 4 (8), pp. 2958-2962.
- . (2006) 'Diffusion of walls in double-walled carbon nanotubes'. Fullerenes Nanotubes and Carbon Nanostructures, 14 (2-3), pp. 215-220.
- . (2006) 'Multi-walled nanotubes: CommensurateIncommensurate phase transition and NEMS applications'. Fullerenes Nanotubes and Carbon Nanostructures, 14 (2-3), pp. 131-140.
- . (2006) 'Pattern formation on carbon nanotube surfaces.'. Phys Rev Lett, United States: 96 (21)
- . (2006) 'Peierls barriers and core properties of partial dislocations in SiC'. Materials Science Forum, 527-529 (PART 1), pp. 359-362.
- . (2006) 'Platelets and the 110 a0 4 {001} stacking fault in diamond'. Physical Review B - Condensed Matter and Materials Physics, 73 (11)
- . (2006) 'Interwall interaction and elastic properties of carbon nanotubes'. Physical Review B - Condensed Matter and Materials Physics, 73 (4)
- . (2006) 'First principles modelling of scroll-to-nanotube defect: Screw-type dislocation'. Materials Science Forum, 527-529 (PART 2), pp. 1583-1586.
- . (2006) 'Electron spectroscopy of carbon materials: Experiment and theory'. Journal of Physics: Conference Series, 26 (1), pp. 149-152.
- . (2001) 'Adatoms and nanoengineering of carbon'.
- . (1998) 'Nitrogen doping in purely sp2 bonded forms of carbon'. The American Physical Society Physical Review B: Condensed Matter and Materials Physics, 57 (2), pp. R661-R665.
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(1996) 'On the graphitization of diamond surfaces: the importance of twins'. Elsevier Diamond and Related Materials, 5 (1), pp. 102-112.Full text is available at: http://epubs.surrey.ac.uk/745034/
Abstract
Ab initio total energy calculations reported recently (M.I. Heggie, C.D. Latham, R. Jones and P.R. Briddon, Phys. Rev. B, 50 (1994) 5937) revealed that the tetrahedrally bonded icosahedral C100 molecule decomposed spontaneously into two concentric fullerenes (C20 and C80). This C100 molecule belongs to a series of structures that may be viewed as the diamond analogues of fullerenes (L. Zeger and E. Kaxiras, Phys. Rev. Lett., 70 (1993) 2920). Since these molecules can be seen to be effectively a heavily twinned molecular diamond, their stability is important in the context of investigating the diamond “111” surface where a twin emerges. We present ab initio self-consistent calculations on a rather small C40H36 molecule representing the core of a twin intersecting two diamond “111” surfaces, and compare the results with those obtained with a non-self-consistent density-functional based tight-binding method. Since the latter is also capable of handling larger and periodic models in a molecular dynamics relaxation, we use it to study the graphitization effect as a function of temperature. We find nearly the same ground state for the small molecule which is clearly due to a graphitization, and find strong surface graphitization for a model of 128 carbon atoms at elevated temperatures. At 2700 K the top layer of this periodic model delaminates completely.
- . (1995) 'Hypothetical C100 molecule and diamond-graphite interface: unstable and metastable states of carbon'. Elsevier Diamond and Related Materials, 4 (4), pp. 528-531.
- . (1994) 'The energetics of hydrogenic reactions at diamond surfaces calculated by a local spin-density functional theoretical method'. Elsevier Diamond and Related Materials, 3 (11–12), pp. 1370-1374.
Conference papers
- . (1997) 'LDF calculations on large fullerenes and onions'. Pennington, NJ : The Electrochemical Society Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, Montreal, Canada: Fullerenes: Chemistry, Physics, and New Directions IX 4, pp. 1141-1150.
- . (1995) 'Local density functional modeling of diamond growth and graphitization'. Pennington, NJ : Electrochemical Society Diamond Materials, Reno, Nevada: Fourth International Symposium on Diamond Materials 4, pp. 643-648.
Book chapters
- . (2000) 'Effective doping in novel sp² bonded carbon allotropes'. in Riedel R (ed.) Handbook of Ceramic Hard Materials Weinheim, Germany : WILEY-VCH Verlag GmbH , pp. 271-285.