In this Letter we study electronic structure of CdmSem quantum rods (QRs) and quantum tubes (QTs) of different sizes. We demonstrate that HOMO-LUMO and optical gaps are higher for quantum tubes than for quantum rods with approximately the same diameters and lengths. In addition we calculate the density of states (DOS) and optical absorption spectra using TDDFT and CIS methods as well as DFT for the DOS calculations. We determine that the DOS and optical spectra are rather different for all samples. The TDDFT and CIS calculations exhibit similar but slightly shifted spectra. The DFT calculations are essentially different from the TDDFT and CIS ones. Thus, we conclude that the DFT method has to be used with care for DOS and optical spectra calculations. (C) 2014 Elsevier B.V. All rights reserved.