First-principles calculations of lattice-strained core-shell nanocrystals

We have examined the properties of CdS-ZnS and ZnS-CdS core-shell nanocrystals over a range of shell thicknesses using a real-space pseudopotential-density functional theory approach. The effect of structural relaxation was shown to be important as it leads to significant changes in the band-gap and frontier orbital localizations. It was also predicted that strains at the core-shell interface are only affected by addition of the first few shell layers, with subsequent layers producing small changes in the strain configuration. This strain saturation gives rise to a ``thin'' shell regime in which both confinement and strain effects contribute to the evolution of the band gap and a ``thick'' shell regime in which band-gap variations from bulk values are strongly dependent on confinement effects but approximately constant with respect to strain.