Structural and electronic properties of lead sulfide quantum dots from screened hybrid density functional calculations including spin-orbit coupling effects

Abstract

We present in this work density functional theory calculations of the structural and electronic properties of (PbS)n nanoparticles with n=4-32. Particular care has been taken on the correct description of their electronic structure by using a hybrid functional including the spin-orbit coupling effects. We demonstrate that the bonding in PbS nanoparticles is quite different from bulk PbS as the six Pb-S bonds around a single Pb atom are found to have a different character while in bulk PbS all Pb-S distances are equivalent. We also relate the geometric structure to the evolution of the HOMO-LUMO gaps and show how the computed electronic properties strongly depend on the functional used. Finally, based on an extrapolation of our results we predict that to obtain the onset of absorption in the infrared region of the spectrum a cubic nanoparticle of ~1.96 nm side length is needed, a result that is in agreement with existing experimental information