Modeling of copper-carbon solid solutions

The atomistic simulations in the framework of the Generalized Simulated Annealing approach (GSA) and classical force fields lead to very reasonable relaxed geometries around the carbon interstitial in O-, T-, and TS-sites. We have thus shown that a highly efficient energy-sampling and relaxation scheme, implemented with tight constraints on a limited volume, provides a powerful 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 and C, predict the relaxed O-site to be more stable than the T-site by ∼1.2 eV, in accordance with general expectations. The TS barrier to O - O diffusion is found to be ∼0.8 eV, at a temperature of 0 K; the TS exhibits a strong local axial distortion of the pseudo-octahedral environment. The Density Functional results indicate a charge transfer of ∼1 e to carbon, mostly from the first neighbor shell, in all relaxed environments studied. Bond-order data show the Cu-C interaction to be bonding in nature, despite the net 'repulsive interaction' leading to a surface state of lower net energy.