R.J. Nicholls D. Nguyen-Manh D.J.H. Cockayne S. Lazar
The unoccupied density of states is simulated for two different experimentally determined C 60 crystal structures. Several theoretical crystal structures are constructed to allow the effects of bond length and relative molecular orientation to be studied. It is found that both have an effect on the unoccupied states, and that the larger effect is c…
PublishedS. P. Fitzgerald D. Nguyen-Manh
We present the first derivation of the analytic expression for the Peierls-Nabarro potential for crowdion migration using the double sine-Gordon model. The analysis is guided by the group-specific trend in the shapes of the periodic lattice potentials calculated for the body-centered-cubic transition metals in groups 5B and 6B of the periodic table…
PublishedS. P. Fitzgerald D. Nguyen-Manh
In this paper we model (111) self-interstitial defects, or crowdions, using an extended version of the analytical Frenkel-Kontorova model. We use a more general potential than the traditional sinusoidal one, and find that it can better describe the lattice potentials experienced by crowdions in the body-centred-cubic transition metals, as calculate…
PublishedP. M. Derlet D. Nguyen-Manh S. L. Dudarev
We investigate the structure and mobility of single self-interstitial atom and vacancy defects in bodycentered- cubic transition metals forming groups 5B vanadium, niobium, and tantalum and 6B chromium, molybdenum, and tungsten of the Periodic Table. Density-functional calculations show that in all these metals the axially symmetric 111 self-inters…
PublishedM. Mrovec R. Gröger A. G. Bailey D. Nguyen-Manh C. Elsässer V. Vitek
We present a bond-order potential BOP for the bcc transition metal tungsten. The bond-order potentials are a real-space semiempirical scheme for the description of interatomic interactions based on the tight-binding approximation. In the hierarchy of atomic-scale-modeling methods the BOPs thus provide a direct bridge between electronic-structure an…
PublishedM. Yu. Lavrentiev R. Drautz D. Nguyen-Manh T. P. C. Klaver S. L. Dudarev
Iron-chromium alloys are characterized by a complex phase diagram, by the small negative enthalpy of mixing at low Cr concentrations in the bcc -phase of Fe, and by the inversion of the short-range order parameter. We present Monte Carlo simulations of the binary Fe-Cr alloy based on the cluster expansion approximation for the enthalpy of the syste…
PublishedM. J. Cawkwell D. Nguyen-Manh D. G. Pettifor V. Vitek
A tight-binding based bond-order potential BOP has been constructed for the fcc transition metal iridium that includes explicitly only d orbitals in the evaluation of the total energy.We show that hybridization between the nearly free electron sp band and the unsaturated covalently bonded d orbitals is important in determining the relative stabilit…
PublishedD. A. Murdick X. W. Zhou H. N. G. Wadley D. Nguyen-Manh R. Drautz D. G. Pettifor
An analytic, bond-order potential BOP is proposed and parametrized for the gallium arsenide system. The potential addresses primary and secondary bonding and the valence-dependent character of heteroatomic bonding, and it can be combined with an electron counting potential to address the distribution of electrons on the GaAs surface. The potential …
PublishedD. Nguyen-Manh A. P. Horsfield S. L. Dudarev
We present an investigation of systematic trends for the self-interstitial atom SIA defect behavior in body-centered cubic bcc transition metals using density-functional calculations. In all the nonmagnetic bcc metals the most stable SIA defect configuration has the 111 symmetry. Metals in group 5B of the periodic table V, Nb, Ta have significantly…
PublishedC. Lang D. J. H. Cockayne D. Nguyen-Manh
Atomistic simulations combining a Monte Carlo algorithm and molecular static relaxations were carried out to predict the alloying profile in pyramid and dome shaped Ge(Si)/Si(001) islands. The results show that the composition profile is dominated by the surface segregation of Ge and segregation of Si to the substrate island interface. Within the i…
Published