Fig. 6: Plots of the Laplacian ∇²ρ(r) and resonance structures.

Plots of the Laplacian ∇²ρ(r) for 1²⁺ (a) and 2²⁺ (b). Red dashed lines indicate areas of charge concentration (∇²ρ(r) < 0), while solid blue lines show areas of charge depletion (∇²ρ(r) > 0). The solid lines connecting the atomic nuclei are the bond paths. Green dots are bond critical points and red dots are ring critical points. c Resonance structures of 1²⁺.