Tight-binding g-factor calculations of CdSe nanostructures

The Landé g factors for CdSe quantum dots and rods are investigated within the framework of the semiempirical tight-binding method. We describe methods for treating both the n-doped and neutral nanostructures, and then apply these to a selection of nanocrystals of variable size and shape, focusing on approximately spherical dots and rods of differing aspect ratio. For the negatively charged n-doped systems, we observe that the g factors for near-spherical CdSe dots are approximately independent of size, but show strong shape dependence as one axis of the quantum dot is extended to form rodlike structures. In particular, there is a discontinuity in the magnitude of the g factor and a transition from anisotropic to isotropic g factor tensor at aspect ratio $\sim \mathrm{1.3.}$ For the neutral systems, we analyze the electron g factor of both the conduction- and valence-band electrons. We find that the behavior of the electron g factor in the neutral nanocrystals is generally similar to that in the n-doped case, showing the same strong shape dependence and discontinuity in magnitude and anisotropy. In smaller systems the g factor value is dependent on the details of the surface model. Comparison with recent measurements of g factors for CdSe nanocrystals suggests that the shape-dependent transition may be responsible for the observations of anomalous numbers of g factors at certain nanocrystal sizes.