Spectroscopic and electronic structure properties of CdSe nanocrystals: spheres and cubes.

In this work we study the electronic structure of CdmSem quantum dots of various sizes and different shapes such as spheres and cubes using DFT, TDDFT, and CIS methods. This work requires a careful computational analysis where a proper exchange-correlation functional has to be chosen to fit the experimental optical gap. We find some differences in the optical and HOMO-LUMO gap values between spheres and cubes. In general, the gaps for the cubes have higher values than those for the spheres. We also calculate optical absorption spectra using the data for energy levels and oscillator strengths for optical transitions. We find that DFT yields some discrepancy in the density of states for the spheres and cubes. However, the density of states calculated by TDDFT and CIS provide better agreement. The results of the calculation can be useful for quantum dots synthesized in laser ablation experiments.