Section through part of a molecular junction. On the left you can see the terminal atoms of the gold electrode, represented in a ball-and-stick model with yellow balls. On the right there is part of the molecule. The red/blue bubbles display the wave function of the transmitting state – a state that carries the electric current when voltage is applied.
Notice, at the terminal atom of the electrode tip (the “apex”), the wave function resembles a butterfly shape. This is the d state (angular momentum l=2) of gold, which plays a key role in the transport of electrons.
You can find more details in
Impact of Electrode Density of States on Transport through Pyridine-Linked Single Molecule Junctions
Adak Olgun, Korytár Richard, Joe Andrew, Evers Ferdinand, Venkataraman Latha