Theoretical study of the molecular and electronic structures of neutral silver bromide clusters (AgBr)n, n=1-9

The structures and UV absorption spectra of (AgBr)(n) clusters (n = 1-9) are investigated in both the gas phase and in a dielectric medium. The structures of clusters were determined at the B3P86 level using a moderate size basis set with full geometry optimization. For clusters with n = 1-6, extensive searches of the potential energy surface yielded only one minimum, while larger clusters displayed two or more minima. Qualitative aspects of the major UV absorption band were also explored. Experimentally, as the clusters grow from monomers to larger systems, this band initially shifts to the blue and then to the red. Our computational results parallel the experimental trends and show that the maximum blue shift occurs at the trimer or the tetramer. The molecular origin of the blue/red shift associated with AgBr cluster growth can be readily explained by examining the orbital interactions which dominate the process and by the structure characteristics of the clusters. Detailed molecular orbital energy level correlation diagrams for the dimerization, trimerization, and tetramerization are also presented.