This investigation can be classified into two main parts (theoretical and experimental). Theoretical investigation is carried out in experimental optical, structure and electrical study of CdSe nanocrystals. In the first part the electronic structure properties of II-VI Zinc-blende CdSe nanocrystals for dimension (1.76-2.34) nm was studied by using Ab-initio Density functional theory (DFT) at the generalized gradient approximation (GGA) level coupled with large unit cell (LUC) method of core atoms (8,16,54,64) for 3D periodic boundary condition (PBC), and in 2D (PBC) calculations was used to simulated oxygenated (001)-(1x1) surface. These properties include total energy, energy gap, cohesive energy, ionicity, valence band width, conduction band width, and highest degeneracy of states were calculated. The energy gap within the range (1.73- 1.77 eV) for core part, while in surface part is smaller than in core part. Two kinds of cells were investigated (8, 64) core atoms with a cubic Bravais multiple Cells and (16, 54) core atoms with a parallelepiped primitive multiple cells. The cohesive energy and ionicity decrease when the number of core atoms increase.