Theoretical Study of the BeH Molecule

An iterative procedure, involving the use of an elliptical basis set, natural orbitals, “pair equations,” and consecutive use of the perturbation and variation methods, was used to calculate the ground‐state energy of the BeH molecule—the ${}^2\Sigma$ state. The energy with the best 50‐configuration wavefunction, at the experimental internuclear separation of 2.5380 a.u., was found to be −15.221 a.u. (experimental = −15.254 a.u.), corresponding to 65% of the experimental dissociation energy. A dipole moment of −0.07 a.u. (−0.18 D) was obtained. Population analysis of the molecular wavefunctions was done to investigate the nature of the chemical bond involved. Less complex calculations involving configuration interaction were also done for the low‐lying excited states at nine different internuclear separations. Potential energy curves were plotted. The transition energy obtained ${(}^2{\mathrm{\Pi \to }}^2\mathrm{\Sigma )}$ was found to be within 1.3% of the experimental value. Transition probabilities were also considered.