Cu_(n-1)Au(n=2—10)团簇结构、静态极化率及吸收光谱的第一性原理研究

First principles study of structures,static polarizabilities and optical absorption spectra of Cu_(n-1)Au(n=2—10) clusters

采用遗传算法,得到贵金属混合团簇Cun-1Au(n=2—10)的稳态结构,并采用分别基于静态及含时的密度泛函理论的第一性原理方法计算了团簇的静态极化率和吸收光谱.由于d电子屏蔽效应的增强,金原子的引入会导致团簇静态极化率的降低,但立体的构型能减小这种影响.基于含时密度泛函理论的第一性原理计算得到的吸收光谱指出,这种屏蔽效应同时导致共振强度的明显下降.d轨道对跃迁贡献的进一步计算,指出d轨道成分是团簇的光激发中的主要贡献者,但d电子的屏蔽作用并不会直接导致在激发中d轨道贡献的提升.针对固定尺寸体系,Cu6-nAun(n=0—6)团簇的研究进一步论证了此观点.计算的光谱与实验值能很好地对应,并且比其他更早的理论计算更为接近实验值.

The structures of Cun-1Au clusters are examined using the genetic algorithm, and the static polarizabilities and optical absorption spectra are investigated by first principles computations within the static and time-dependent versions of the density functional theory. The static polarizabilities decrease after being doped by one Au atom due to the strengthened screening effect of d electrons, which can also be weakened by three-dimensional structures. The optical spectra computed within the time-dependent density functional theory indicate that the screening effect also leads to the quenching of oscillator strengths. A deeper analysis of d-orbit indicates d-orbit is the main contributor in the optical excitation while its growing up is not directly influenced by the strengthened screening effect. The research on Cu6-nAun （n = 0--6） clusters in a fixed size system verifies our arguments further. Our calculation results are in good agreement with the experimental data on the optical absorption spectra, which are closer to the experimental data than the earlier theoretical results.