Study of the electronic and optical properties of undoped sodium iodide using density functional theory DFT

The electronic and optical properties of undoped sodium iodide (NaI) were investigated. This study was carried out by the method of the Density Functional Theory (DFT) implemented by Quantum Expresso. The approximation used is the GGA (Generalized Gradient Approximation). The determined lattice parameter is 4.4485 Å. According to the results obtained, the electronic and optical properties are those of an indirect-gap semiconductor. The gap obtained is 3.712 eV. The electronic properties are affected by the 2s state of iodine and the 3p state of iodine I. With regard to optical properties, the evolution of the real part of the dielectric function ε1(ω) shows that incident electromagnetic waves are mainly reflected by the medium in a certain energy region. The material then exhibits metallic behaviour. This can provide layers of protection against radiation in these energy regions. The imaginary part ε2(ω) of the dielectric function shows several peaks certainly due to the transitions of electrons between 3p states of sodium, 2s states of iodine and 3p states of iodine but especially 2s states of iodine and 3p states of iodine. We can therefore say that the electronic transition takes place between the 2s state of I and the 3p state of I. These studies on the electronic and optical properties prove that sodium iodide (NaI) is of considerable interest.