Electric Field Effects on Neutral Gold Clusters Au2-10: A First-Principles Theoretical Survey of the First- and Second-Order Hyperpolarizabilities

Herein we report the density functional theory (DFT) calculations of nonlinear optical (NLO) properties of neutral gold clusters Aun (n=2-10) applying long-range corrected LC-M06L functional and Los-Alamos National Laboratory double-ζ polarized basis set. The effects of the incident frequency on the first and second-order hyperpolarizability together with the influence of the external electric field on the frontier orbitals of neutral gold clusters are investigated. It is found that the application of external electric field can increase or decrease the gap energy of neutral gold clusters depending on the direction and magnitude of the applied field. More importantly, by correctly controlling the direction and magnitude of the external electric field, reactive gold clusters having low gap energies can be achieved. Furthermore, the external electric field has more important effect on the virtual orbitals of gold hexamer and decreases the energy of these orbitals along the directions parallel to the molecular plane, resulting in low-energy excitations. The low-energy excitations are expected to play important role in the high second-order hyperpolarizability and better response to the applied field. The third-order nonlinear (NLO) properties of gold hexamer are also strongly affected by the frequency of the incident light and thus can be tuned using the incident frequency for applications. The present work may propose new strategies for enhancing the nonlinear optical response of neutral gold clusters.