The van der Waals potential of the magnesium dimer

The ground state van der Waals potential of the magnesium dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the three dispersion coefficients C-6, C-8, and C-10 are available from accurate ab initio calculations. The other two are the Born-Mayer parameters in A exp(-bR). In this paper, we show that A and b can be determined from the self-consistent Hartree-Fock calculations and the experimental dissociation energy D-0. The predicted well depth D-e and equilibrium distance R-e are in nearly perfect agreement with the experiment. In fact, the entire potential energy curve, which is given by a single analytic function, is in excellent agreement with the pointwise potential energies constructed from the spectroscopic measurements in the interval of 6a(0)-14a(0) and in good agreement with the experimental repulsive potential determined from Franck-Condon factors of the bound-free transitions for R less than 6a(0). The reduced potential of Mg-2 is analyzed in terms of its components, and the number of terms in the dispersion series necessary for convergence is investigated. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3479392]