  Modifying the optoelectronic properties of nanostructured materials through
introduction of dopant atoms has attracted intense interest. Nevertheless, the
approaches employed are often trial and error, preventing rational design. We
demonstrate the power of large-scale electronic structure calculations with
density functional theory (DFT) to build an atlas of preferential dopant sites
for a range of M(II) and M(III) dopants in the representative III-V InP magic
sized cluster (MSC). We quantify the thermodynamic favorability of dopants,
which we identify to be both specific to the sites within the MSC (i.e.,
interior vs surface) and to the nature of the dopant atom (i.e., smaller
Ga(III) vs larger Y(III) or Sc(III)). These observations motivate development
of maps of the most and least favorable doping sites, which are consistent with
some known experimental expectations but also yield unexpected observations.
For isovalent doping (i.e., Y(III)/Sc(III) or Ga(III), we observed stronger
sensitivity of the predicted energetics to the type of ligand orientation on
the surface than to the dopant type, but divergent behavior is observed for
whether interior doping is favorable. For charge balancing with M(II) (i.e., Zn
or Cd) dopants, we show that the type of ligand removed during the doping
reaction is critical. We show that limited cooperativity with dopants up to
moderate concentrations occurs, indicating rapid single-dopant estimations of
favorability from DFT can efficiently guide rational design. Our work
emphasizes the strong importance of ligand chemistry and surface heterogeneity
in determining paths to favorable doping in quantum dots, an observation that
will be general to other III-V and II-VI quantum dot systems generally
synthesized with carboxylate ligands.
