where A represents a nucleus, and 𝑍 A and 𝑹 A are the charge and position of the nucleus A, respectively. The ESP is generally insensitive to the level of sophistication, e.g., the size of the basis set and the level of electron correlation, since it depends directly on the electron density (ρ = |Ψ| 2 ). 2D ESP was rendered by Visual Molecular Dynamics (VMD) and/or Gaussview 69 software packages.