As demonstrated by Johnson et al. , noncovalent interactions are associated with regions where s(r) → 0, with stripe-like features in s(r) vs. ρ(r) plots serving as fingerprints for NCIs (see Figure ). NCIs can be distinguished as attractive or repulsive via the second eigenvalue λ 2 of the electron-density Hessian matrix (λ 1 < λ 2 < λ 3 ), where λ 2 < 0 indicates attraction, and λ 2 > 0 signifies repulsion . The product ρ(r)sign(λ 2 ) effectively captures interaction strength, and NCIs can be visualized as 3D isosurfaces of s(r). The gradient isosurfaces are colored according to ρ(r)sign(λ 2 ), where blue indicates strong attractive interactions (such as hydro- gen bonding), green represents weak vdW attractions, and red denotes steric repulsion.