A5022100820- Advanced Chemical Physics Studies
- High-pressure geophysics and materials
- Quantum, superfluid, helium dynamics
- X-ray Diffraction in Crystallography
- Physics of Superconductivity and Magnetism
- Crystallization and Solubility Studies
- Boron and Carbon Nanomaterials Research
- Surface and Thin Film Phenomena
- Inorganic Fluorides and Related Compounds
- Quantum and electron transport phenomena
- Diamond and Carbon-based Materials Research
- Catalysis and Oxidation Reactions
- Catalytic Processes in Materials Science
- Semiconductor materials and devices
- Superconductivity in MgB2 and Alloys
- Semiconductor materials and interfaces
- Semiconductor Quantum Structures and Devices
- Machine Learning in Materials Science
- Advanced Physical and Chemical Molecular Interactions
- Crystallography and molecular interactions
- Rare-earth and actinide compounds
- Spectroscopy and Quantum Chemical Studies
- Atomic and Molecular Physics
- Graphene research and applications
- Silicon Carbide Semiconductor Technologies
Cavendish Hospital
2003-2021
University of Cambridge
2011-2020
Lancaster University
2016
Carnegie Mellon University
2016
Universidad de La Laguna
2015
University College London
2009-2012
Tokyo University of Science
2011
Australian Synchrotron
2011
Japan Science and Technology Agency
2008
University of the Basque Country
2003-2004
This article describes the variational and fixed-node diffusion quantum Monte Carlo methods how they may be used to calculate properties of many-electron systems. These stochastic wave-function-based approaches provide a very direct treatment many-body effects serve as benchmarks against which other techniques compared. They complement less demanding density-functional approach by providing more accurate results deeper understanding physics electronic correlation in real materials. The...
It is essential to know the arrangement of atoms in a material order compute and understand its properties. Searching for stable structures materials using first-principles electronic structure methods, such as density-functional-theory (DFT), rapidly growing field. Here we describe our simple, elegant powerful approach searching with DFT, which call ab initio random (AIRSS). Applications discovering solids, point defects, surfaces, clusters are reviewed. New results iron on graphene,...
Advances in the accuracy and efficiency of first-principles electronic structure calculations have allowed detailed studies energetics materials under high pressures. At same time, improvements resolution powder x-ray diffraction experiments more sophisticated methods data analysis revealed existence many new unexpected high-pressure phases. The most complete set theoretical experimental obtained to date is for group-IVA elements group-IIIA--VA IIB--VIA compounds. Here authors review...
Room-temperature superconductivity has been a long-held dream and an area of intensive research. Recent experimental findings at 200 K in highly compressed hydrogen (H) sulfides have demonstrated the potential for achieving room-temperature H-rich materials. We report first-principles structure searches stable clathrate structures rare earth hydrides high pressures. The peculiarity these lies emergence unusual H cages with stoichiometries H_{24}, H_{29}, H_{32}, which atoms are weakly...
High-pressure phases of silane SiH4 are predicted using first-principles electronic structure methods. We search for low-enthalpy structures by relaxing from randomly chosen initial configurations, a strategy which is demonstrated to work well unit cells containing up at least ten atoms. predict that will metallize higher pressures than previously anticipated but might show high-temperature superconductivity experimentally accessible pressures.
The sixth blind test of organic crystal structure prediction (CSP) methods has been held, with five target systems: a small nearly rigid molecule, polymorphic former drug candidate, chloride salt hydrate, co-crystal and bulky flexible molecule. This seen substantial growth in the number participants, broad range giving unique insight into state art field. Significant progress treating molecules, usage hierarchical approaches to ranking structures, application density-functional...
We investigate the pressure-induced metal-insulator transition of silicon in diamond structure. Quasiparticle theory (QPT) calculations are performed within GW approximation, and Kohn-Sham (KST) results obtained by using an exchange-correlation potential derived from self-energy operator, not common local-density approximation (LDA). In both KST LDA, metallization occurs at a much larger volume than QPT. These suggest that point Fermi surface electrons necessarily those real system.
We use first-principles calculations to study structural, vibrational, and superconducting properties of H_{2}S at pressures P≥200 GPa. The inclusion zero-point energy leads two different possible dissociations H2S, namely 3H2S→2H3S+S 5H2S→3H3S+HS2, where both H3S HS2 are metallic. For H3S, we perform nonperturbative anharmonic effects within the self-consistent harmonic approximation show that strongly overestimates electron-phonon interaction (λ≈2.64 200 GPa) Tc. Anharmonicity hardens H─S...
We have performed first-principles pseudopotential calculations for H-terminated Si wires with thicknesses from 12 to 23 \AA{}, calculating the band gaps and optical matrix elements. Comparison effective-mass theory shows that latter is valid wider than \AA{}. used our data analyze luminescent properties of highly porous fabricated by electrochemical etching wafers in HF-based solutions.
Following on from the success of previous crystal structure prediction blind tests (CSP1999, CSP2001, CSP2004 and CSP2007), a fifth such collaborative project (CSP2010) was organized at Cambridge Crystallographic Data Centre. A range methodologies used by participating groups in order to evaluate ability current computational methods predict structures six organic molecules chosen as targets for this test. The first four targets, two rigid molecules, one semi-flexible molecule 1:1 salt,...
This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wave functions capable achieving very high accuracy. The algorithms intrinsically parallel well-suited to petascale computers, computational cost scales as a polynomial number particles. A guide systems topics which have been investigated using these is given. bulk article devoted an overview basic methods, forms optimisation...
Density-functional-theory calculations and a structure-searching method are used to identify candidate high-pressure phases of nitrogen. We find six structures which calculated be more stable than previously studied at some pressures. Our four new molecular give insight into the most efficient packings nitrogen molecules high pressures, we predict two nonmolecular very
A form of Jastrow factor is introduced for use in quantum Monte Carlo simulations finite and periodic systems. Test data are presented atoms, molecules, solids, including both all-electron pseudopotential atoms. We demonstrate that our able to retrieve a large fraction the correlation energy.
Quantum Monte Carlo (QMC) calculations are only possible in finite systems and so solids liquids must be modeled using small simulation cells subject to periodic boundary conditions. The resulting finite-size errors often corrected data from local-density functional or Hartree-Fock calculations, but systematic remain after these corrections have been applied. results of our jellium QMC for containing more than 600 electrons confirm that the residual significant decay very slowly as system...
We present a new method for efficient, accurate calculations of many-body properties periodic systems. The main features are (i) use real-space/imaginary-time representation, (ii) avoidance any model form the screened interaction $W$, (iii) exact separation $W$ and self-energy $\ensuremath{\Sigma}$ into short- long-ranged parts, (iv) novel analytical continuation techniques in energy domain. computer time scales approximately linearly with system size. give results jellium silicon, including...
An inhomogeneous backflow transformation for many-particle wave functions is presented and applied to electrons in atoms, molecules, solids. We report variational diffusion quantum Monte Carlo (VMC DMC) energies various systems study the computational cost of using functions. find that transformations can provide a substantial increase amount correlation energy retrieved within VMC DMC calculations. The significantly improve their nodal surfaces.
We report self-consistent density-functional calculations of the energy and enthalpy silicon carbon in fully relaxed complex B-8 structure (bcc with 8 atoms per cell). find to be unstable Si, slightly higher than diamond $\ensuremath{\beta}$-tin phases. is found a stable phase C above 12 Mbar, which new stability limit for diamond.
We analyze the problem of eliminating finite-size errors from quantum Monte Carlo (QMC) energy data. demonstrate that both (i) adding a recently proposed [S. Chiesa et al., Phys. Rev. Lett. 97, 076404 (2006)] correction to Ewald and (ii) using model periodic Coulomb (MPC) interaction [L. M. Fraser B 53, 1814 (1996); P. R. C. Kent 59, 1917 (1999); A. J. Williamson 55, R4851 (1997)] are good solutions removing effects in cubic systems provided exchange-correlation (XC) hole has converged with...
The authors investigate, up to the fourth-nearest neighbour, interaction energies J1 J4 between SiC double layers by calculating total of five polytypes with norm-conserving pseudopotentials. They find J1=1.89 mod J2 negative. This is very close multi-phase degeneracy point J1=2 in ANNNI model at T=0 where an infinite number are degenerate. third-(J3) and fourth-(J4) neighbour interactions turn out be small but they stabilise phase (3) (in Zhdanov notation) which has lowest energy those...
Quantum mechanical calculations of the surface stress tensor at aluminum (111) and (110) surfaces are presented. In each case is tensile, favoring contraction in plane surface. This tensile caused by smoothing electronic wave functions crystal