Structure search for B7Cr2 clusters: Inverse sandwich structure for the global minimum

Abstract

In this work, we employ density functional theory (DFT) to explore the structure of boron clusters doped with two chromium atoms (B${}_7$Cr${}_2$). The results show that the most stable structure is a bipyramidal configuration formed by a B${}_7$ ring coordinated with two Cr atoms, similar to recently reported B${}_7$M${}_2$ analogues. The most stable clusters favor doublet states, while higher-spin states compete closely with the most stable configurations. The stability favors a decrease in the effective coordination number but an increase in the average bond distances. The results based on bonding orbital analyses show that the coordination of the Cr${}_2$ dimer into the B${}_7$ ring involves both orbital and electrostatic stabilization. The structural and electronic properties exhibit notable differences between the global minimum and the higher energy isomers. Additionally, the results of AdNDP bonding analysis and NICS indicate a deshielding region at the center of the structure with long-range characteristics, highlighting the antiaromatic nature of B${}_7$Cr${}_2$.