The optimized geometries of C18 and (BN)nC(18-2n) (n = 1-9) and their Cartesian coordinates are shown in Figure and Table , respectively. There is no imaginary frequency in all vibrational modes of the molecules studied, confirming the optimized geometries are local minima on their respective potential energy surfaces (PESs). (TDOS) is positively correlated with their number of units.