Phthalocyanine (${\mathrm{H}}_2\mathrm{Pc}$) based molecules are widely used as model systems in scanning tunneling microscopy (STM) based surface characterizations. In the present work, we carried out theoretical simulations on the STM images of ${\mathrm{H}}_2\mathrm{Pc}$ and deprotonated phthalocyanine (${\mathrm{HPc}}^{-}$) molecules by combining density functional theory calculations with Bardeen's approximation. The obtained STM images for the frontier molecular orbitals of the molecular systems resemble nicely the previously reported experimental features. It was found that the deprotonation process can lead to more profound effects for the lowest unoccupied molecular orbital (LUMO). Particularly, the ringlike feature in the central cavity of ${\mathrm{H}}_2\mathrm{Pc}$ as found in the LUMO was reduced to a half ring that is most bright in the position of the removed proton in ${\mathrm{HPc}}^{-}$, which corrects the intuitive assignment in the previous studies. The position and shape of the half ring feature in the central cavity coincide with the spatial distribution of the high negative values in the electrostatic potential of the molecule. Detailed analysis suggests that such a feature should be attributed to the asymmetric distribution of the wave function of the LUMO in the cavity of the deprotonated ${\mathrm{HPc}}^{-}$. Raman images for vibrational modes associated with the central H atoms of the two molecular systems were also simulated based on an effective field Hamiltonian. The good correspondence between the Raman images and the molecular vibrations suggests it could be applied to decisively identify the position of the remaining H atom in the ${\mathrm{HPc}}^{-}$.

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• Adsorption
• Density functional theory
• First-principles calculations
• Scanning tunneling microscopy
• Surface-enhanced Raman spectroscopy