The HOMA analysis of aromaticity in the corrugated BPN sheet (Figure ) shows the effect of the adsorption from another perspective. Due to the corrugation, the planarity around the adsorption site vanishes, resulting in HOMA values below -5 (antiaromatic). The effect is strong throughout the whole row of 6-and 4-rings. Only minor differences occur between 6-4 and 8-4. An increase in aromaticity is observed for the 6-rings, whereas it decreases for the 8-rings. This local formation of aromatic 6-rings is more pronounced for 6-4. The effect is most substantial near the adsorption site and can be correlated to a simple Lewis picture. The bond alterations, corresponding to the single and double bonds of kekulene, correlate with the localization of double bonds (Figure ). albeit not in a ring structure. Consequently, the difference in the adsorption energies (-140 vs. -115 kJ mol -1 ) can be attributed to the still intact aromaticity of the 6-rings in 6-4 which is lifted for 8-4.