THE INVESTIGATION ON ELECTRONIC STRUCTURE AND SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF II–VI SEMICONDUCTOR CLUSTERS BY TIME-DEPENDENT DENSITY FUNCTIONAL THEORY

Abstract

Time-dependent density functional theory (TD-DFT) formalism is employed to calculate the electronic spectra of A 3 B 3 II–VI semiconductor clusters based on the geometrical structures optimized at DFT-B3LYP level. Moreover, their second-order nonlinear optical (NLO) properties are performed by TD-B3LYP combined with sum-over-states (SOS) formula. The calculation results indicate that it is necessary to consider the effective core potential and electron correlation effects when the basis sets are chosen for the heavy atoms. In addition, the results show that the transition energies and HOMO–LUMO gaps of the A 3 B 3 II–VI semiconductor clusters decrease, while the second-order nonlinear optical responses increase with the increasing of VI-group ionic radius. As a result, the SOS formula is valuable to calculate the βμ in the summation of 120 states. Meanwhile, charge transfers from the π bonding to π anti-bonding orbitals between II and VI group atoms significantly contribute to the second-order NLO properties.