Modeling of copper-carbon solid solutions

The atomistic simulations in the framework of the Generalized Simulated Ann ealing approach (GSA) and classical force fields lead to very reasonable re laxed geometries around the carbon interstitial in O-, T-, and TS-sites. We have thus shown that a highly efficient energy-sampling and relaxation sch eme, implemented with tight constraints on a limited volume, provides a pow erful steering mechanism for selection of geometries suitable for detailed investigation by first-principles methods. The results, based upon harmonic interactions between Cu atoms and a van der Waals interaction between Cu a nd C, predict the relaxed O-site to be more stable than the T-site by simil ar to 1.2 eV, in accordance with general expectations. The TS barrier to O- O diffusion is found to be similar to 0.8 eV, at a temperature of 0 K; the TS exhibits a strong local axial distortion of the pseudo-octahedral enviro nment. The Density Functional results indicate a charge transfer of similar to 1 e to carbon, mostly from the first neighbor shell, in all relaxed env ironments studied. Bond-order data show the Cu-C interaction to be bonding in nature, despite the net 'repulsive interaction' leading to a surface sta te of lower net energy. (C) 2000 Elsevier Science Ltd. All rights reserved.