Erratum: Improved real-space genetic algorithm for crystal structure and polymorph prediction [Phys. Rev. B 77, 134117 (2008)]

In our earlier work, there was an error in the derivation of the spherically averaged scattering intensity, presented as Eq. (5) in the original paper. This equation should have readΛ(kr)=∑n=1Nρ′(n)2+2∑n=1N∑m>nNρ′(n)ρ′(m)j0(kr∣∣∣∣rn−rm|), (5)where j0(r) is the spherical Bessel function of the first kind

Quantum diffusion of H/D on Ni(111)—A partially adiabatic centroid MD study

We present the results of a theoretical study of H/D diffusion on a Ni(111) surface at a range of temperatures, from 250 K to 75 K. The diffusion is studied using both classical molecular dynamics and the partially adiabatic centroid molecular dynamics method. The calculations are performed with the hydrogen (or deuterium) moving in 3D across a static nickel surface using a novel Fourier interpolated potential energy surface which has been parameterized to density functional theory calculations. The results of the classical simulations are that the calculated diffusion coefficients are far too small and with too large a variation with temperature compared with experiment. By contrast, the quantum simulations are in much better agreement with experiment and show that quantum effects in the diffusion of hydrogen are significant at all temperatures studied. There is also a crossover to a quantum-dominated diffusive regime for temperatures below ∼150 K for hydrogen and ∼85 K for deuterium. The quantum diffusion coefficients are found to accurately reproduce the spread in values with temperature, but with an absolute value that is a little high compared with experiment

Simultaneous Prediction of the Magnetic and Crystal Structure of Materials Using a Genetic Algorithm

We introduce a number of extensions and enhancements to a genetic algorithm for crystal structure prediction, to make it suitable to study magnetic systems. The coupling between magnetic properties and crystal structure means that it is essential to take a holistic approach, and we present for the first time, a genetic algorithm that performs a simultaneous global optimisation of both magnetic structure and crystal structure. We first illustrate the power of this approach on a novel test system—the magnetic Lennard–Jones potential—which we define. Then we study the complex interface structures found at the junction of a Heusler alloy and a semiconductor substrate as found in a proposed spintronic device and show the impact of the magnetic interface structure on the device performance

DL_MG : A Parallel Multigrid Poisson and Poisson–Boltzmann Solver for Electronic Structure Calculations in Vacuum and Solution

The solution of the Poisson equation is a crucial step in electronic structure calculations, yielding the electrostatic potential—a key component of the quantum mechanical Hamiltonian. In recent decades, theoretical advances and increases in computer performance have made it possible to simulate the electronic structure of extended systems in complex environments. This requires the solution of more complicated variants of the Poisson equation, featuring nonhomogeneous dielectric permittivities, ionic concentrations with nonlinear dependencies, and diverse boundary conditions. The analytic solutions generally used to solve the Poisson equation in vacuum (or with homogeneous permittivity) are not applicable in these circumstances, and numerical methods must be used. In this work, we present DL_MG, a flexible, scalable, and accurate solver library, developed specifically to tackle the challenges of solving the Poisson equation in modern large-scale electronic structure calculations on parallel computers. Our solver is based on the multigrid approach and uses an iterative high-order defect correction method to improve the accuracy of solutions. Using two chemically relevant model systems, we tested the accuracy and computational performance of DL_MG when solving the generalized Poisson and Poisson–Boltzmann equations, demonstrating excellent agreement with analytic solutions and efficient scaling to ∼10^9 unknowns and 100s of CPU cores. We also applied DL_MG in actual large-scale electronic structure calculations, using the ONETEP linear-scaling electronic structure package to study a 2615 atom protein–ligand complex with routinely available computational resources. In these calculations, the overall execution time with DL_MG was not significantly greater than the time required for calculations using a conventional FFT-based solver

Huge power factor in p-type half-Heusler alloys NbFeSb and TaFeSb

NbFeSb is a promising thermoelectric material which according to experimental and theoretical studies exhibits a high power factor of up to 10 mW/(m.K^2) at room temperature and ZT of 1 at 1000 K. In all previous theoretical studies, κ_latt is calculated using simplified models, which ignore structural defects. In this work, we calculate κ_latt by solving the Boltzmann Transport Equation and subsequently including the contributions of grain boundaries, point defects and electron-phonon interaction. The results for κ_latt and ZT are in excellent agreement with experimental measurements. In addition, we investigate theoretically the thermoelectric properties of TaFeSb. The material has recently been synthesised experimentally, thus conrming the theoretical hypothesis for its stability. This encourages a full-scale computation of its thermoelectric performance.Our results show that TaFeSb is indeed an excellent thermoelectric material which has an unprecedentedly high power factor of 16 mW/(m.K^2) at room temperature and ZT of 1.5 at 1000 K

Theoretical study of core-loss electron energy-loss spectroscopy at graphene nanoribbon edges

A systematic study of simulated atomic-resolution Electronic Energy-Loss Spectroscopy (EELS) for different graphene nanoribbons (GNRs) is presented. The results of ab initio studies of carbon 1s core-loss EELS on GNRs with different ribbon edge structures and different hydrogen terminations show that theoretical core-loss EELS can distinguish key structural features at the atomic scale. In addition, the combination of polarized core-loss EELS with symmetry resolved electronic partial density of states (PDOS) calculations can be used to identify the origins of all the primary features in the spectra. For example, the nature of the GNR edge structure (armchair, zigzag, etc) can be identified, along with the degree of hydrogenation. Hence it is possible to use the combination of ab initio calculations with high resolution, high energy transmission core-loss EELS experiments to determine the local atomic arrangement and chemical bonding states (i.e. a structural fingerprint) in GNRs, which is essential for future practical applications of graphene