Chirality of small niobium clusters

Abstract

We report on time-dependent density functional theory calculations to study the chiroptical properties of small $$\hbox {Nb}_{{9}}$$ clusters and their corresponding van der Waals $$\hbox {Nb}_{{9}}\hbox {Ar}_{n}$$ complexes. The three most stable 9-atom structures considered in the literature are analyzed, and we obtain their lowest-energy atomic configurations, UV–Vis response, and for the first time, the electronic circular dichroism (ECD) spectra of the systems. Excitation energies, as well as oscillator and rotational strengths are calculated using the M06 exchange-correlation functional together with a mixed basis approach where all electron DGDZVP and Def2SV basis are employed for Nb and Ar atoms, respectively. In all cases, the UV–Vis spectra look very similar and are characterized by the formation of a main absorption maxima located at $$\sim 240\hbox { nm}$$ ; however, the distribution of simulated ECD signals strongly depends on the geometrical structure of the clusters. Our calculated ECD bands show precise features that cover the experimentally accessible 200–300 nm range and extend near the visible part of the spectra, a fact that allows us to distinguish between different niobium cluster geometries. However, weighted averages of calculated ECD spectra for different $$\hbox {Nb}_{{9}}$$ clusters reveal that isomerization effects might lead to a notable increase/reduction in the intensity of CD lines since the simulated bands could add or cancel each other.