Nonadditive potentials between three Rydberg atoms

We calculate interaction potentials between three rubidium Rydberg atoms in the absence of external fields. Several three-atom states are considered: vertical bar nS, nS, n'S > and vertical bar nD, nD, nD > (36 < n < 75). Among the considered states, nonadditive potentials appear in the S states if n not equal n' or if vertical bar n - n'vertical bar is small, and also in D states. Interatomic potentials are nonadditive when they induce intensive mixing between three-atom states of the same zero-order energy. The consideration of nonadditive potentials may add a new dimension to the research into Rydberg atoms.