In a recent Letter [PRL 96, 226802 (2006)], Dalpian and Chelikowsky claimed that formation energies of Mn impurities in CdSe nanocrystals increase as the size of the nanocrystal decreases, and argued that this size dependence leads to "self-purification" of small nanocrystals. They presented density-functional-theory (DFT) calculations showing a strong size dependence for Mn impurity formation energies, and proposed a general explanation. In this Comment we show that several different DFT codes, pseudopotentials, and exchange-correlation functionals give a markedly different result: We find no such size dependence. More generally, we argue that formation energies are not relevant to substitutional doping in most colloidally grown nanocrystals.
Cite
@article{arxiv.0805.0280,
title = {Comment on "Self-Purification in Semiconductor Nanocrystals"},
author = {M. -H. Du and S. C. Erwin and Al. L. Efros and D. J. Norris},
journal= {arXiv preprint arXiv:0805.0280},
year = {2008}
}