Abstract
Zinc blend (zb) and wurtizite (wz) structure of cadmium selenide (CdSe) is determined using density-functional theory within local density approximation (LDA), generalized gradient approximation (GGA), Hubbard-correction (GGA+U) and Hybrid functional approximation (PBE0 or HSE06). The first principle pseudopotential plane wave is used and the relaxed atomic position for the CdSe in zb and wz structure was obtained by using total energy and force minimization method following the Hellmann Feynman approach. The convergence test of total energy with respect to cutoff energy and k-point sampling is performed . The equilibrium lattice constant and unit cell volume of CdSe in both phases are calculated and the obtained value is compared` with experimental values. In addition the band gap of CdSe is analyzed using DFT within LDA, GGA, DFT+U and PBE0 to approximate the unknown exchange correlation functional. The band gap values obtained using LDA and GGA are severally under estimated due to their poor approximation of exchange-correlation potential. This problem was improved by using projector augmented-wave pseudopotential within Hubbard-correction (GGA+U) and the hybrid functional approximation. Optical properties: complex and real parts of dielectric function, energy loss spectrum and absorption coefficient of CdSe in both ZB and WZ phase were studied.
Highlights
Cadmium selenide (CdSe) is a semiconductor compound of the II-VI family which crystalizes in zinc blend and wurtizite phases [1]
Its value for ideal WZ CdSe structure is 0.375. It shows that our calculations in accord with local density approximation (LDA), PBE, DFT + U and PBE0 are in good agreement with previous theoretical and experimental results
The values of lattice constants obtained using LDA, PBE, DFT + U and PBE0 approximations are in good agreement with experimental results
Summary
Cadmium selenide (CdSe) is a semiconductor compound of the II-VI family which crystalizes in zinc blend and wurtizite phases [1]. The electronic and structural properties of CdSe are studied using LDA [15]. The elastic, electronic and lattice dynamical properties CdSe is studied using LDA [17]. In addition to this the band gap of CdSe is calculated using EV-GGA [18]. These LDA based computational results of the band gap are found to be lower than the experimental band gap values. In present study the electronic, structural and optical properties of ZB- and WZ- phase of CdSe are determined using LDA, GGA, GGA + U and PBEO methods.
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