DFT Calculations of InP Quantum Dots: Model Chemistries, Surface Passivation, and Open-Shell Singlet Ground States

Density functional theory (DFT) calculations on large clusters of indium phosphide are presented. Several quantum dot-sized models, (NH3)(64)(InP)(117), (COOH2)(45)(InP)(117), (In-Cl-3)(29)(InP)(147), and (ZnCl2)(29)(InP)(147), were passivated with organic or inorganic ligands; in some systems, both types were used. Initial results with the PBE1PBE functional proved puzzling as many clusters were initially found to have open-shell paramagnetic ground states, which is not sensible for nanoparticles of a direct band-gap semiconductor. In the case of QDs passivated with organic ligands, implementation of a robust geometry optimization procedure demonstrated that these findings were due to localization to metastable states and that the ground states are in fact diamagnetic singlets. However, the nonstoichiometric inorganic-passivated clusters (InCl3)(29)(InP)(147) and (ZnCl2)(29)(InP)(147) have ground nonet and septet states, respectively. Examination of the molecular orbitals revealed non-Aufbau state filling, suggesting the potential for open-shell singlet ground states, which is supported by calculations at the more robust M06-2x level of theory. Experimental evidence for paramagnetic or open-shell singlet ground states was not realized, which may be due to a mixture of inorganic and organic passivations.

Automated summary

Density functional theory calculations were conducted on large clusters of indium phosphide, revealing different ground state spin properties depending on whether the clusters were passivated with organic or inorganic ligands. Further molecular orbital analysis and optimization procedures showed that the ground states are diamagnetic singlets with the potential for open-shell singlet states in certain nonstoichiometric inorganic-passivated clusters.