The effects of surface normal vibration on the effective pair interaction for 4He atoms in the second layer of a bilayer has been calculated. The single-particle potential for atoms in the second layer included pair interactions between the second-layer 4He atom and fixed carbon atoms in the graphite plus the pair interaction between the second-layer 4He atom and an oscillating first layer. The shift in the pair interaction between the second-layer atoms is about 10-15% of the "bare" interaction. Rough estimates were made of the effect upon the Van der Waals constants for the second-layer imperfect gas and these estimates were compared to empirical values.
Title
Effective pair interaction and the Van der Waals constants for second-layer helium atoms in bilayer films
Novaco, A. D. (1976). "Effective pair interaction and the Van der Waals constants for second-layer helium atoms in bilayer films." Physical Review B 13 (7): 3194–3196.