Research Interests

Current projects include:

• First principles thermodynamics of bulk phases, surfaces and interfaces in realistic environments
• Multiscale modelling of materials ageing
• Molecular magnetism, electronics and spintronics
• First principles theory of electrochemical interfaces
• New models of photoelectron spectroscopy and quantum efficiency

Publications

Highlights

A Previously Proposed Magnetic Structure of Carbon is Unstable The structure and stability of a pure carbon structure involving mixed sp2-sp3 bonding, long thought to be ferromagnetic, is examined. The structure is found to be unstable with respect to a barrier free transformation to a non magnetic polymorph. Stability of the Ferromagnetic State in a Mixed sp2-sp3 Carbon System L. Pisani, B. Montanari, N. M. Harrison Phys. Rev. B 80 104415 (2009)
	Structural Transformations in Graphene A combination of hybrid exchange density functional theory and transmission electron microscopy with high spatial and temporal resolution is used to develop a model of the structural transformations in graphene sheets induced by beam damage at 80keV. Structural Transformations in Graphene Studied with High Spatial and Fast Temporal Resolution Jamie H. Warner, Mark H. Rummeli, Ling Ge, Thomas Gemming, Barbara Montanari, Nicholas M. Harrison, Bernd Buchner, G. Andrew D. Briggs Nature Nanotechnology 4 500 (2009)
Bipolarons, Orbital Ordering and Magnetism in Ti4O7 Hybrid exchange density functional theory calculations are used to provide a consistent description of the low, intermediate and high temperature phases of Ti4O7. Strong on-site Coulomb interactions and electron phonon coupling produce zero spin polarons in the LT phase. In the IT phase a subset of the bipolarons dissociate but the electrons remain highly localised. The Metal-Insulator Transition in the Ti4O7 Magneli Phase Leandro Liborio, Giuseppe Mallia, Nicholas M Harrison Phys. Rev. B 79 245133 (2009)
	Spin Transport in Carbon Peapod Structures Electron spins on fullerene cages may be a suitable system for realising a scalable quantum bit (qubit) array. A possible implementation of this concept is to use carbon nanotubes to encapsulate a chain of endohedral fullerenes such as Sc@C82 to form a peapod structure. The spins generated by electron donation from the Sc ion are localised on the fullerene chains. The spin interactions, electronic structure and dynamics of this system has been studied. Effects of Doping on Electronic Structure and Correlations in Carbon Peapods L. Ge, John H. Jefferson, B. Montanari, N. M. Harrison, D. G. Pettifor and G. A. D. Briggs, ACS Nano ASAP (2009) DOI 10.1021/nn8008454 Modelling Spin Interactions in Carbon Peapods using Hybrid Exchange Density Functional Theory L. Ge, B. Montanari, J. H. Jefferson, D. G. Pettifor, N. M. Harrison, G.A.D. Briggs, Phys. Rev. B 77 235416 (2008) Dynamics of Paramagnetic Metallofullerenes in Carbon Nanotube Peapods J. H. Warner, A. A. R. Watt, L. Ge, K. Porfyrakis, T. Akachi, H. Okimoto, Y. Ito, A. Ardavan, B. Montanari, J. H. Jefferson, N. M. Harrison, H. Shinohara, G. A. D. Briggs Nano Lett. 8 1005 (2008)
Molecular Magnets Materials based on transition-metal-tetracyanoethylene (TCNE) are of particular interest as molecular magnets as they display a rich range of magnetic behaviour and have relatively high critical temperatures. The vanadium material is remarkable in that it has magnetic order above room temperature but is X-ray amorphous. Hybrid exchange DFT has been used to develop a structural model and to explain the exceptionally strong magnetic coupling. Density functional study of the magnetic coupling in V(TCNE)2 Giulia C. De Fusco, Leonardo Pisani, Barbara Montanari, Nicholas M. Harrison , Phys. Rev. B. 79 085201 (2009)
	Computational Characterisation of Fluorination Catalysts High surface area AlF3 is a new highly active fluorination catalyst but its structure and reaction sites are poorly understood. First principles thermodynamics has been used to charaterise the alpha and beta phases of AlF3. Potential Lewis acid sites are identified and their acidity quantified through NH3 binding energies CO frequency shifts. Steps, Microfacets and Crystal Morphology: An ab initio Study of β-AlF3 Surfaces, A Wander, C L Bailey, S Mukhopadhyay, B G Searle and N M Harrison J. Phys. Chem. C. 112, 6517 (2008) Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption, C.L. Bailey, A. Wander, S. Mukhopadhyay, B.G. Searle, and N.M. Harrison J. Chem. Phys. 128 224703 (2008) Adsorption of HF and HCl on the β-AlF3 surface, C.L. Bailey, A. Wander, S. Mukhopadhyay, B.G.Searle and N.M. Harrison, Phys. Chem. Chem. Phys. 10 2918 (2008)

Earlier Work:

• The theory of electron diffraction and surface vibrations in surface structure determination
  Phys. Rev. Lett. 94 246102, 2005


• A demonstration of spin singlet formation in MgTi₂O₄ and the observation of a chiral dimerisation pattern
  Phys. Rev. Lett., 92, 061801, 2004


• The development of a new model for the role of thermodynamic and kinetic restrictions on the intercalation of lithium into titania
  Phys. Rev. Lett., 86, 3811, 2001
  Phys. Rev. B, 235423 2002
  


• Demonstrations of the operation of a charge transfer mechanism for the stability of ZnO polar surfaces through surface metallisation and of water adsorbtion and reconstruction on the stability of NiO and MgO polar surfaces
  Phys. Rev. Lett., 86, 3811, 2001
  Phys. Rev. B., 68, 233405, 2003


• The discovery, through first principles simulations, of a new ultra hard oxide - cottunite structured titania
  Nature, 410, 253, 2001
  Phys. Rev. B, 65 224112, 2002
  

Software Development

The group is involved in the development of software for predictive simulation, analysis of experimental data and visualisation. In particular;

• CRYSTAL.
  An all electron Gaussian basis set code for the first principles simulation of periodic systems.
• CASTEP.
  A plane-wave, pseudopotential code for the first principles simulation of systems periodic in three dimensions.
• DLVisualize.
  A graphical user interface for a variety of materials simulation codes.
• DL-EXCURV.
  A new code for the interpretation of X-ray adsorbtion spectra.