Theory of sigma bond resonance in flat boron materials

Abstract

In chemistry, theory of aromaticity or pi bond resonance plays a central role in intuitively understanding the stability and properties of organic molecules. Here we present an analogue theory for sigma bond resonance in flat boron materials, which allows us to determine the distribution of two-center two-electron and three-center two-electron bonds without quantum calculations. Based on this theory, three rules are proposed to draw the Kekule-like bonding configurations for flat boron materials and to explore their properties intuitively. As an application of the theory, a simple explanation of why neutral borophene with similar to 1/9 hole has the highest stability and the effect of charge doping on borophene's optimal hole concentration is provided with the assumption of sigma and pi orbital occupation balance. Like the aromaticity theory for carbon materials, this theory greatly deepens our understanding on boron materials and paves the way for the rational design of various boron-based materials.