Spectroscopic constants of H₂ using Monte Carlo methods

We have computed the spectroscopic constants w_e, w_ex_e, α_e, and B_e of the ground state of H₂ using two methods. In the first method, a highly accurate potential energy surface was generated using explicitly correlated wave functions and variational Monte Carlo techniques. We calculated the vibrational-rotational energies from this surface and then obtained the spectroscopic constants by fitting these energies to a simple equation. In the second method, the spectroscopic constants were determined from local derivatives of the energy with respect to the internuclear distance. These derivatives have also been calculated using variational Monte Carlo techniques. For this system we find that the first method yields spectroscopic constants that are in excellent agreement with experiment. We also find that the second method, although slightly less accurate, is extremely well suited to Monte Carlo calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004