Double electrostatics

Second electrostatics (ACS Nano 12, 5274−5283 (2018)) can be applied by keyword tip_base, which has two parameters: multipole and charge. (The original electrostatics is still handled by keywords tip and charge) I.e. the metal tip-base dipole, due to Smoluchowski effect, of 1.5 Debye (Nano Lett. 16, pp 1974–1980 (2016)) can be applied by using tip_base 'pz' 0.44. This line has to be in the params.ini during calculations of generateElFF.py, relaxed_scan.py and plot_results.py.

The actual metal tip-base charge is applied only in the last script (Fz -> df conversion only!) and does not have any effect on the relaxation or IETS!

Image illustrating electrostatic field around CO-tip - from left to right (1-3 and 5 are analytical models) 1) Electrostatic potential around quadrupole on oxygen. 2) Potential around dipole of the metallic tip-base. 3) Electrostatic potential of the whole system. 4) DFT calculated potential around CO-tip on metallic cluster, taken from Supplementary Information of Nat. Commun. 9, 122 (2018). 5) z-component of the electric field around the whole (CO-tip + metallic tip-base) system. Green point (at the corner of triangle) depicts the last atom of the metallic tip-base, while gray and orange points illustrates positions of carbon and oxygen, respectively. The orange circle represents van der Waals radius of the oxygen atom

Note: According to experience, the double electrostatics is important mainly for materials with strong polarization, while for (most of) molecules on metal substrates it has minor effect as you can see on PTCDA/Ag(111) simulations without/with (left/right) metal tip-base dipole and quadrupole: Q: -0.3/0.0/0.3 (top/middle/bottom), sigma 0.71.