An improved QM/MM approach for metals

We present an improved quantum mechanical (QM) and molecular mechanical (MM) coupling method for the study of metallic systems. The improved method is based on the earlier work of Choly et al (2005 Phys. Rev. B 71 094101). In this approach, quantum mechanical treatment is spatially confined to a small region, surrounded by a larger molecular mechanical region. This approach is particularly useful for systems where quantum mechanical interactions in a small region, such as lattice defects or chemical impurities, can affect the macroscopic properties of a material. We discuss how the coupling across the different scales can be accomplished efficiently and accurately for metals. The method is tested by performing a multiscale simulation of bulk aluminium (Al) where the coupling errors can be easily analysed. We then apply the method to study the core structure and Peierls stress of an edge dislocation in Al. (Some figures in this article are in colour only in the electronic version)