Optical Properties of Wurtzite CdSe Nanorods from First Principles Simulations*

The tunability of optical properties of colloidal semiconductor nanocrystals by size, shape, and composition make them attractive for applications ranging from bioimaging to solar energy conversion. Growth conditions can be tuned to yield anisotropic nanorods with one-dimensional quantum confinement and controllable thickness, length, and aspect ratios. These structural parameters together enable precise control over spectroscopic properties. With empirical lengths typically between 5–100 nm, calculating the ground state electronic properties of nanorods is prohibitively expensive with current implementations of density functional theory (DFT) due to the large system size and a lack of periodic boundary conditions. In contrast, nanowires can be described with periodic boundary conditions in the axial direction, enabling calculation of electronic properties using a small unit cell. We use DFT to compute the ground state electronic structure and simulate the optical properties of wurtzite CdSe nanowires with varying wire thickness. We compare calculated nanowire spectra with experimental spectra of nanorods with similar thicknesses but different aspect ratios at the band edge to understand how thickness and aspect ratio independently affect nanorod optical properties.