Construction, assessment, and application of a bond-order potential for iridium

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 stabilities of the close-packed structures and that this effect can be accurately captured through the use of a central force term. The BOP is found to provide an excellent description of the equilibrium properties of iridium, including its negative Cauchy pressure that is fitted using a many-body repulsive term. The transferability of the BOP is assessed by calculating energy differences between different crystal structures, the energetics of the tetragonal and trigonal deformation paths, the phonon spectra, stacking fault, and vacancy formation energies. Comparison of the results of these studies with either experiments or first principles calculations is found to be good. We also describe briefly the application of the constructed BOP to the atomistic simulation of the core structure of the screw dislocation that led to an explanation of the anomalous deformation and fracture behavior exhibited of iridium. Comments Copyright American Physical Society. Reprinted from Physical Review B, Volume 73, Issue 6, Article 064104, February 2006, 13 pages. Publisher URL: http://dx.doi.org/10.1103/PhysRevB.73.064104 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/84 Construction, assessment, and application of a bond-order potential for iridium M. J. Cawkwell,1,* D. Nguyen-Manh,2,† D. G. Pettifor,3 and V. Vitek1,‡ 1Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104-6202, USA 2EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom 3Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom Received 6 September 2005; revised manuscript received 19 December 2005; published 8 February 2006 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 stabilities of the close-packed structures and that this effect can be accurately captured through the use of a central force term. The BOP is found to provide an excellent description of the equilibrium properties of iridium, including its negative Cauchy pressure that is fitted using a many-body repulsive term. The transferability of the BOP is assessed by calculating energy differences between different crystal structures, the energetics of the tetragonal and trigonal deformation paths, the phonon spectra, stacking fault, and vacancy formation energies. Comparison of the results of these studies with either experiments or first principles calculations is found to be good. We also describe briefly the application of the constructed BOP to the atomistic simulation of the core structure of the screw dislocation that led to an explanation of the anomalous deformation and fracture behavior exhibited of iridium. DOI: 10.1103/PhysRevB.73.064104 PACS number s : 61.50.Ah, 61.72.Bb, 71.20.Be, 62.20.Fe