Exceptional points in multichannel resonance quantization

We derive from the quantization condition of a multichannel resonance problem the behaviour of resonance energies close to an exceptional point (EP) where two resonance energies coalesce. The formalism is applied to a one-dimensional model of the molecular ion H₂ ⁺. Although the approach does not use a matrix diagonalization procedure, all known results about exceptional points are present, including the transfer from one resonance to another when following a loop encircling the EP. We study how the resonance wave functions behave along loops around the EP, as well as the associated geometric phases.