Angular forces in group-VI transition metals: Application to W(100)

On the work function of the surface Mo(0 0 1) and its temperature dependence: an ab initio molecular dynamics study

Ab initio molecular dynamics simulations in NVT ensemble have been performed to investigate the finite temperature structure of the Mo(0 0 1) surface and its effect on work function (ϕ). In accord with previous experimental and theoretical work, our simulations predict that a termination with a stable reconstruction pattern is formed at T  =  123 K. This pattern vanishes when temperature is increased to 423 K or 623 K and a disordered surface phase is formed whose time average corresponds to a bulk-like termination. Our results demonstrate that the surface relaxation is an important factor contributing to thermal variation of ϕ. At the lowest temperature, at which a stable reconstruction pattern is formed, the work function is found to increase by  ∼0.23 eV compared to relaxed unreconstructed surface. The disappearance of stable reconstruction pattern at elevated temperatures leads to a decrease of ϕ by  ∼0.07 eV. In contrast, the values computed for a non-reconstructing surface Mo(1 1 0) at T  =  123 K, 423 K and 623 K are found to be nearly identical to the zero temperature value, which is a consequence of restricted atomic motion due to high packing density in this surface.

Interatomic Interactions for BCC Metals Based on the Low Order Moments of the Density of States

A model of the energetics of bcc transition metals based on the low-order moments of the electronic density of states is presented. The new feature of the model is an additional energy term related to the fourth moment of the density of states. This term reflects the coarse shape of the density of states. The model is tested by the computation of point defect properties, phonon dispersions, structural energy differences and surface properties. The results are compared to experiment, ab-initio calculations and other model interatomic potentials. The results indicate that the inclusion of the fourth moment term in the energy does not significantly improve the description of properties of the bulk bcc metals. However, the fourth moment term substantially improves the description of large deviations from the bcc bulk such as surfaces and alternative crystal structures.

Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals

Atomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.

Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.

Angular-dependent matrix potentials for fast molecular-dynamics simulations of transition metals

The significance of the part played by the angular-dependent components of forces associated with d-d bonding between atoms in a transition metal has long remained a subject of debate. While almost all the large-scale molecular dynamics simulations of collision cascades and radiation damage in transition metals and alloys are currently performed using spherically symmetric many-body potentials, density functional calculations exhibit a highly anisotropic pattern of charge density deformation in and around the core of interstitial atom defects. This paper describes a fast second-order matrix recursion-based algorithm for including effects of angular anisotropy of d-d bonds in a large-scale molecular dynamics simulation.