Description Of Interatomic Forces Research Articles

A critical assessment of interatomic potentials for ceria with application to its elastic properties revisited

Doped ceria is an important electrolyte material for solid oxide fuel cell applications due to its high oxygen diffusivity. From the perspective of atomic scale computational modelling, the prediction of properties and consequently underlying mechanisms often rely on classical potential for the description of interatomic forces acting within ceria. The recent paper of Xu et al. (Solid State Ionics 181:551, 2010) reviewed several potential models and stated that the potential parameters of Grimes et al. (Philos. Mag. A 72:651, 1995) lead to poor reproduction of ceria’s thermal expansion coefficient. Here we show that this assessment is erroneous and that the Grimes et al. potential model adequately describes thermal expansion in CeO2. The calculated results are discussed in view of experimental results.

Directional versus central-force bonding in studies of the structure and glide of 1/2⟨111⟩ screw dislocations in bcc transition metals

In this paper, we address the differences between Finnis–Sinclair potentials and bond-order potentials (BOPs) when studying 1/2⟨111⟩ screw dislocations in bcc transition metals, specifically Mo and W. These two types of potentials differ in that the former is central-force, whereas the latter include angular bonding. The cores of 1/2⟨111⟩ screw dislocations have two variants, one invariant with respect to the ⟨101⟩ diad and the other not. Hence, the latter core is degenerate. The BOPs always lead to the invariant type, whereas for Finnis–Sinclair potentials both variants occur. However, the symmetry of the core does not play a decisive role in the glide of dislocations. It is the description of interatomic forces that governs both the core structure and the glide behaviour of dislocations. The general characteristics of dislocation glide, the twinning–antitwinning asymmetry and a lower Peierls stress for tension than compression are the same for both types of potentials. Whereas the results obtained with BOPs are similar for the two cases studied, Finnis–Sinclair potentials lead to a broader variety. Particularly, the slip plane at 0 K is always {110} for BOPs but it is either {110} or {112} for Finnis–Sinclair potentials. The reason is that, in the latter case, the core configuration and core transformations are less constrained than in the former case. Hence, in bcc transition metals the BOPs are a more reliable description of atomic interactions than Finnis–Sinclair potentials, but when the d band does not play any important role, the Finnis–Sinclair potentials are fully applicable.

Alloying behaviour of binary transition metal systems

Abstract The properties of A – B binary alloys are controlled by the mixed AB interaction potentials. The interfaces between two different metals are investigated for fictive mixed potentials spreading from A-type to B-type nature. The elemental AA and BB potentials are fixed. The tendencies towards formation of ordered structures on one side, and separation of phases on the other side are discussed. A description of interatomic forces respecting metallic bonding character in many-body potentials is used. This approach can be helpful for applications of alloy potentials in models with complex structures of extended defects such as dislocations and grain boundaries and in the assessment of their behaviour.

Displacive Phase Transformations

Shear deformation and shuffling of atomic planes are elementary mechanisms of collective atomic motion that take place during displacive phase transformations. General displacements of atomic planes are examined, i.e. -surface type calculations extensively used for the stacking faults and crystal dislocations are applied to single plane shuffling and alternate shuffling of every other atomic plane producing in combination with homogeneous deformation the hcp structure (martensitic type) from the initial bcc structure (austenitic type). Similar approach considering shear type planar displacements leads to the Zener path between the bcc and fcc lattices. The effect of additional deformation required to obtain the close-packed atomic arrangements is examined as well. Finally, the influence of volume modification on phase transitions is investigated. The energies of various structural configurations are calculated using many-body potentials for the description of interatomic forces. Such atomic models are tested to check their suitability for investigation of the role of interfaces in the displacive structural transitions.

A molecular dynamics study of the critical thickness of Ge layers on Si substrates

Epitaxial growth can occur layer-by layer or by islanding. The mode of growth depends on the surface energies of the substrate and the epilayer. In cases of the growth of strained layers, the strain energy of the film also needs to be taken into account. This may results in the formation of misfit dislocations at the interface. Also where strain effects are important, initial layer-by-layer growth can become three-dimensional through islanding. Using the method of molecular dynamics and a many-body description of interatomic forces, we have made a study of the comparative energies of strained-relieved epilayers as well as (111) faceted islands of Ge on Si(001). We conclude that the critical thickness for this system is around 3 monolayers.

Interatomic potentials for atomistic studies of defects in binary alloys

A description of interatomic forces in pure metals and disordered, substitutional binary alloy systems is developed on an empirical basis. The description is formulated for use in atomistic studies of lattice defects. In both pure metals and alloys the total internal energy is expressed as the sum of two terms: a pair potential term and a term that depends only on the average density of the material. It is assumed that in pure metals all of the cohesive energy is provided by the second term. The empirical parameters employed in the construction of potentials for pure metals are the cohesive energy and elastic constants. For alloys the different atomic sizes and electronegativities of the alloying elements are taken into account, and the potentials are self-consistently adjusted to the enthalpy of mixing for corresponding alloy concentrations. In addition all potentials are required to satisfy the equilibrium conditions governing mechanical stability of the corresponding crystal structures. Reasonable agreement is obtained between calculated dependences of elastic constants on alloy concentration and available experimental data. Several derived potentials for pure metals and alloys are presented, in particular those employed in a subsequent atomistic study of grain boundary segregation. The scheme can be used to construct approximate descriptions of atomic interactions in specific binary systems, or for the construction of model systems in which the required empirical data are taken as variables.

Brillouin scattering from GaS under hydrostatic pressure up to 17.5 GPa

Brillouin scattering in GaS crystals had been measured under hydrostatic pressures up to 17.5 GPa. Frequency shifts of the Brillouin lines give the pressure dependence of the elastic constants C11 and C33, and the index birefringence. Exponents derived from Murnaghan’s equation of state are compared with a Lennard-Jones description of interatomic forces in GaS.