Exploration on stability, aromaticity, and potential energy surface of planar BnC2 (n = 3-8)

► The lowest-energy isomers of even-n BnC2 clusters have high stability. ► BnC2 (n = 3-8) clusters exhibit polycyclic to wheel-like structure transition. ► The growth pattern and bonding nature of BnC2 (n = 3-8) are revealed. ► The thermodynamic and kinetic stability of BnC2 (n = 3-8) is examined. ► The aromaticity of some BnC2 isomers (n = 3-8) is analyzed and discussed.