Density functional theory modeling of PbSe nanoclusters: Effect of surface passivation on shape and composition

The energy of three crystallographic faces of the PbSe lattice, with Miller indices (100), (110), and (111), is computed at the density functional theory level with a double-ζ polarized basis set. The addition energy of different organic ligands on the three faces is computed at the same level both in periodic infinite slabs and in finite clusters to explore the relative affinities and the possible modifications of the stability order of the faces. Neutral ligands are found to have the greatest affinity for (110), while propionate anion binds most strongly to (111) face: in the last case the stability order of the pure surfaces can be reversed by the presence of ligands. The prevalence of different faces is related to the shape of PbSe nanoclusters, and a model is proposed to explain the excess of Pb atoms found in nonstoichiometric clusters by some experiments.