Toward Automated Variational Computation of Rovibrational Resonances, Including a Case Study of the H₂ Dimer

A general and semi-automatic technique, based on the complex absorbing potential (CAP) method, is developed for the variational computation and identification of rotational-vibrational resonance states. This technique is an extension of a method introduced by Tremblay and Carrington ( J. Chem. Phys. 2005, 122, 244107 ), and it employs the damped eigenvectors of a CAP-modified Hamiltonian as a basis to describe resonance wave functions. The low-lying resonances of the weakly bound Ar·NO⁺ complex are computed with the new and the traditional CAP techniques to test the new algorithm. As an additional, more challenging test case, the bound and resonance rovibrational states of the H₂ dimer, the latter with both negative and positive binding energies, are determined, corresponding to different rotational excitations of the H₂ monomers. Resonances above the first few dissociation channels of (H₂)₂ are computed with the new and the traditional CAP methods, revealing some new, assigned resonance quantum states not reported in the literature.