Towards the ab initio determination of strictly diabatic states, study for(NaRb)(+)

A generalization of the effective metric approach is proposed and applied b oth for the calculation of radial couplings and for the determination of di abatic states along a single coordinate using the formalism of variational effective Hamiltonian theory. The application to the ionic molecule NaRb+ s hows that strictly diabatic states are obtained even for very short distanc es where a huge number of crossings are observed. Polarization and electron ic delocalization effects are estimated. A comparison with various diabatiz ation methods is performed. The proposed method brings a significant improv ement with respect to the existing ones. (C) 1999 American Institute of Phy sics. [S0021-9606(99)30913-2].