The diagonal correction to the Born-Oppenheimer approximation: Its effect on the singlet-triplet splitting of CH2 and other molecular effects
Abstract
The prediction of the diagonal correction to the Born-Oppenheimer approximation is now possible by ab initio analytic methods, as has recently been shown by Yarkony and Lengsfield. At the general restricted Hartree-Fock (GRHF) level of approximation, the procedure is straightforward: solutions of the coupled perturbed Hartree-Fock equations (CPHF) and some overlap integrals are all that are required. This correction is evaluated for a series of small molecules with various basis sets: H2O, H2O+, CH2, HCF, H+5, and F2. It is interesting to observe that the value of this correction (0.11 kcal) for the singlet-triplet splitting of CH2 is larger than the relativistic correction, and that the theoretical value for Tnre (BO)≡9.23±0.20 kcal has come even closer to the best ab initio prediction of 9.4 kcal.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- April 1986
- DOI:
- 10.1063/1.450020
- Bibcode:
- 1986JChPh..84.4481H