Zhengzheng Chen

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.

Multiplane-induced widening of stacking faults in fcc metals

Using an ab initio-based parametric dislocation dynamics approach we show that Shockley partials on successive glide planes greatly assist the widening of stacking faults (SFs) in Al and Ag. This effect is amplified when all trailing partials are pinned. Subsequent placement of Shockley partials on adjacent planes enhances further the widening of the SF width. In sharp contrast, dislocations with zero net Burgers vector across three successive planes form very compact cores in both Al and Ag, in agreement with recent experiments.

The crucial role of chemistry on mobile properties of dislocation

Dislocation–solute interactions are ubiquitous in solids, yet their dual nature in strengthening or softening the material is not well understood. Results of a novel concurrent multiscale approach reveal that the local environment of W solutes in Ta has a dramatic effect both on the dislocation mobility and slip paths. W solutes can enhance or reduce the mobility, and may result in spontaneous dislocation glide. The atomistic mechanism responsible for the dual nature of solutes is elucidated.