M. C. Payne

University of Cambridge, Cambridge, ENG, United Kingdom

Are you M. C. Payne?

Claim your profile

Publications (158)606.41 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Plane wave basis sets are widely used in ab initio electronic structure calculations even though such an expansion in terms of extended states does not provide a natural way of quantifying local atomic properties. To overcome this deficiency we have implemented a scheme for projection of plane wave states onto a localised basis set. This approach is used to calculate atomic charges and bond populations, and is illustrated by application to a selection of small molecules. Finally, we calculate the changes in these quantities induced by adsorption of a molecule onto a zeolite substrate. Thus, using the procedure described in this paper, plane wave calculations can yield the same information as traditional quantum chemical methods.
    Molecular Physics 12/2010; 89(2):571-577. · 1.67 Impact Factor
  • Source
    M. D. SEGALL, M. C. PAYNE, R. N. BOYES
    [Show abstract] [Hide abstract]
    ABSTRACT: An ab initio density functional theory study is reported of the conformational energy map of acetylcholine, with respect to the two central dihedral angles of the molecule. The acetylcholine molecule pays a central role in neurotransmission and has been studied widely using semi-empirical computational modelling. The ab initio results are compared with a number of previous investigations and with experiment. The ab initio data indicate that the most stable conformation of acetylcholine is the trans, gauche arrangement of the central dihedral angles. Furthermore, Mulliken population analysis of the electronic structure of the molecule in this conformation indicates that the positive charge of the molecule is spread over the exterior of the cationic head of the molecule.
    Molecular Physics 12/2010; February 20(1998):365-370. · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The atomistic simulation of many processes in materials involves large-size model systems where different levels of complexity need to be described simultaneously. While accurate quantum mechanical simulations of large-size systems are usually not affordable, less computationally intensive classical models are not suitable for the description of many chemical processes. Hybrid (quantum/classical) modelling schemes are required in these circumstances. Here, we describe the “Learn on the fly” (LOTF) hybrid molecular dynamics scheme. Some technical aspects of this technique are illustrated through a series of examples of its applications to multiscale processes in silicon KeywordsQuantum/classical atomistics-Hybrid modeling-Multiscale computations
    03/2010: pages 1-23;
  • Journal of the American Chemical Society, v.132, 5993-6000 (2010). 01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: When a brittle material is loaded to the limit of its strength, it fails by the nucleation and propagation of a crack. The conditions for crack propagation are created by stress concentration in the region of the crack tip and depend on macroscopic parameters such as the geometry and dimensions of the specimen. The way the crack propagates, however, is entirely determined by atomic-scale phenomena, because brittle crack tips are atomically sharp and propagate by breaking the variously oriented interatomic bonds, one at a time, at each point of the moving crack front. The physical interplay of multiple length scales makes brittle fracture a complex 'multi-scale' phenomenon. Several intermediate scales may arise in more complex situations, for example in the presence of microdefects or grain boundaries. The occurrence of various instabilities in crack propagation at very high speeds is well known, and significant advances have been made recently in understanding their origin. Here we investigate low-speed propagation instabilities in silicon using quantum-mechanical hybrid, multi-scale modelling and single-crystal fracture experiments. Our simulations predict a crack-tip reconstruction that makes low-speed crack propagation unstable on the (111) cleavage plane, which is conventionally thought of as the most stable cleavage plane. We perform experiments in which this instability is observed at a range of low speeds, using an experimental technique designed for the investigation of fracture under low tensile loads. Further simulations explain why, conversely, at moderately high speeds crack propagation on the (110) cleavage plane becomes unstable and deflects onto (111) planes, as previously observed experimentally.
    Nature 11/2008; 455(7217):1224-7. · 38.60 Impact Factor
  • I. J. Robertson, M. C. Payne, V. Heine
    [Show abstract] [Hide abstract]
    ABSTRACT: Ab initio calculations are presented of the cohesive energies of aluminium in a number of diverse hypothetical structures which span a wide range of the coordination number, C, from C = 0 to C = 12. The calculations have been performed to investigate the nature of multi-atom bonding, its dependence on C and to form a database for testing and developing empirical and semi-empirical models. The results support the saturation of cohesive energy for large C predicted by several simple theoretical models. Calculations on the same structures using semi-empirical schemes suggest that these methods might have a greater degree of accuracy than had previously been believed.
    EPL (Europhysics Letters) 07/2007; 15(3):301. · 2.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An overview is presented of the method used to parallelize a set of total energy pseudopotential codes on a 64-node i860 Meiko Computing Surface and a 32-node Intel iPSC/860 Hypercube. These codes have been used to calculate the surface energies and relaxed structures of the 3 × 3, 5 × 5 and 7 × 7 Takayanagi reconstructions of the (111) surface of silicon. It is found that the 7 × 7 reconstruction has the lowest energy and that structural trends across the series of reconstructions can be related to the degree of charge transfer from the adatoms to the rest atoms.
    Physica Scripta 01/2007; 1992(T45):265. · 1.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Now that the modeling of simple semiconductor systems has become reliable, accurate and routine, attention is focusing on larger scale, more complex simulations. Many of these necessarily involve multiscale aspects and can only be tackled by addressing the different length scales simultaneously. We discuss some of the types of problems that require multiscale approaches. Finally we describe the LOTF (learn-on-the-fly) hybrid scheme with a series of examples to show its versatility and power.
    11/2006: pages 193-212;
  • G. Moras, G. Csanyi, M. C. Payne, A. De Vita
    [Show abstract] [Hide abstract]
    ABSTRACT: We review the main features of a recently proposed molecular dynamics method in which quantum mechanical calculations are embedded in a classical force model within a unified scheme free of boundary region and transferability problems. The scheme is based on the idea of augmenting a parametrized analytic force model by incorporating in it the quantum mechanical information necessary to compute accurate trajectories. This is achieved through a suitable fitting procedure in which the parameters of a classical inter-atomic force field are adjusted at run time to reproduce high-accuracy results which are computed separately on system subsets by tight-binding or DFT-based “black box” computing engines.
    Physica B Condensed Matter 01/2006; 376:936-939. · 1.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts. We extrapolate a common low activation energy of 0.23-0.4 eV, much lower than for thermal deposition. The carbon diffusion on the catalyst surface and the stability of the precursor molecules, C2H2 or CH4, are investigated by ab initio plane wave density functional calculations. We find a low activation energy of 0.4 eV for carbon surface diffusion on Ni and Co (111) planes, much lower than for bulk diffusion. The energy barrier for C2H2 and CH4 dissociation is at least 1.3 eV and 0.9 eV, respectively, on Ni(111) planes or step edges. Hence, the rate-limiting step for plasma-enhanced growth is carbon diffusion on the catalyst surface, while an extra barrier is present for thermal growth due to gas decomposition.
    Physical Review Letters 08/2005; 95(3):036101. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We review recent progress in the field of multiscale hybrid computer simulations of materials, and present an overview of a novel scheme that links arbitrary atomistic simulation techniques together in a truly seamless manner. Rather than constructing a new hybrid Hamiltonian that combines different models, we use a unique short range classical potential and continuously tune its parameters to reproduce the atomic trajectories at the prescribed level of accuracy throughout the system.
    Journal of Physics Condensed Matter 06/2005; 17(27):R691. · 2.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The CASTEP code for first principles electronic structure calculations will be described. A brief, nontechnical overview will be given and some of the features and capabilities highlighted. Some features which are unique to CASTEP will be described and near-future development plans outlined.
    05/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe and test a novel molecular dynamics method which combines quantum-mechanical embedding and classical force model optimization into a unified scheme free of the boundary region, and the transferability problems which these techniques, taken separately, involve. The scheme is based on the idea of augmenting a unique, simple parametrized force model by incorporating in it, at run time, the quantum-mechanical information necessary to ensure accurate trajectories. The scheme is tested on a number of silicon systems composed of up to approximately 200 000 atoms.
    Physical Review Letters 11/2004; 93(17):175503. · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the nitrogen substitutional impurity in semiconducting zigzag and metallic armchair single-wall carbon nanotubes using ab initio density functional theory. At low concentrations (less than 1 at. %), the defect state in a semiconducting tube becomes spatially localized and develops a flat energy level in the band gap. Such a localized state makes the impurity site chemically and electronically active. We find that if two neighboring tubes have their impurities facing one another, an intertube covalent bond forms. This finding opens an intriguing possibility for tunnel junctions, as well as the functionalization of suitably doped carbon nanotubes by selectively forming chemical bonds with ligands at the impurity site. If the intertube bond density is high enough, a highly packed bundle of interlinked single-wall nanotubes can form.
    Physical Review Letters 10/2003; 91(10):105502. · 7.73 Impact Factor
  • Source
    M. I. J. Probert, M C Payne
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a systematic methodology for the accurate calculation of defect structures in supercells which we illustrate with a study of the neutral vacancy in silicon. This is a prototypical defect which has been studied extensively using ab initio methods, yet remarkably there is still no consensus about the energy or structure of this defect, or even whether the nearest neighbour atoms relax inwards or outwards. In this paper we show that the differences between previous calculations can be attributed to supercell convergence errors, and we demonstrate how to systematically reduce each such source of error. The various sources of scatter in previous theoretical studies are discussed and a new effect, that of supercell symmetry, is identified. It is shown that a consistent treatment of this effect is crucial to understanding the systematic effects of increasing the supercell size. This work therefore also presents the best converged ab initio study of the neutral silicon vacancy to date. Comment: 18 pages, 5 figures, requires RevTex4
    Physical Review B 01/2003; · 3.66 Impact Factor
  • The Journal of Physical Chemistry. 04/2002; 99(17).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: First-principles simulation, meaning density-functional theory calculations with plane waves and pseudopotentials, has become a prized technique in condensed-matter theory. Here I look at the basics of the suject, give a brief review of the theory, examining the strengths and weaknesses of its implementation, and illustrating some of the ways simulators approach problems through a small case study. I also discuss why and how modern software design methods have been used in writing a completely new modular version of the CASTEP code.
    Journal of Physics Condensed Matter 03/2002; 14(11):2717. · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The quantitative modeling of many surface processes, such as diffusion or chemical reactions, requires accurate knowledge of free energy profiles. The need to go beyond the internal energy is especially important in entropy-controlled processes which may happen at both high (the thermally-activated regime) and low (the quantum tunneling regime) temperatures. We present results for a thermally-activated process, namely, the formation of the first intermediate in the methanol-to-gasoline process, catalyzed by acidic zeolites. At high temperatures of 700 K, the entropic contribution cannot be correctly evaluated in the harmonic approximation and we use ab initio thermodynamic integration within density functional theory. We find that, at reaction temperatures, the entropic contribution qualitatively alters the free energy profile. Different transition states are found from the internal energy and free energy profiles. The entropic contribution varies significantly along the reaction coordinate and is responsible for stabilizing the products and for lowering the energy barrier. An outlook is given for a proper treatment of entropically-controlled processes in both the thermally-activated and quantum regimes.
    01/2002;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A comparison between experimental and theoretical electron energy loss near edge structure (ELNES) of B and N K edges in cubic boron nitride is presented. The electron energy loss spectra of cubic boron nitride particles were measured using a scanning transmission electron microscope. The theoretical calculation of the ELNES was performed within the framework of density functional theory including single particle core-hole effects. The results suggest that core-hole effects can be adequately incorporated into the plane-wave pseudopotential method to produce striking agreement with the best available experimental spectra.
    Physical review. B, Condensed matter 08/2001; 64(11). · 3.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a theoretical study of the formation of the first intermediate, dimethyl ether, in the methanol to gasoline conversion within the framework of an ab initio molecular dynamics approach. The study is performed under conditions that closely resemble the reaction conditions in the zeolite catalyst including the full topology of the framework. The use of the method of thermodynamic integration allows us to extract the free-energy profile along the reaction coordinate. We find that the entropic contribution qualitatively alters the free-energy profile relative to the total energy profile. Different transition states are found from the internal and free energy profiles. The entropy contribution varies significantly along the reaction coordinate and is responsible for stabilizing the products and for lowering the energy barrier. The hugely inhomogeneous variation of the entropy can be understood in terms of elementary processes that take place during the chemical reaction. Our simulations provide new insights into the complex nature of this chemical reaction.
    Chemistry 07/2001; 7(12):2521-7. · 5.83 Impact Factor

Publication Stats

9k Citations
606.41 Total Impact Points

Institutions

  • 1992–2010
    • University of Cambridge
      • • Department of Physics: Cavendish Laboratory
      • • Department of Chemistry
      Cambridge, ENG, United Kingdom
  • 1998
    • Technical University of Denmark
      København, Capital Region, Denmark
  • 1985–1998
    • Massachusetts Institute of Technology
      • Department of Physics
      Cambridge, Massachusetts, United States
  • 1997
    • Imperial Valley College
      South Kensington, Maryland, United States
  • 1993
    • Keele University
      Newcastle-under-Lyme, England, United Kingdom