A quantum Monte Carlo perturbational study of the He–He interaction

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Abstract
Using a recently proposed quantum Monte Carlo method the exact first‐, second‐, and third‐order Rayleigh–Schrödinger interaction energies of the He–He interaction have been calculated for internuclear distances in the range 1.5‐ to 7.0 bohr. Putting together these new data with the best ab initio results available, the relative importance of the different contributions appearing in the perturbational expansion of the He–He interaction energy is discussed. In particular, the results show that the third‐order Rayleigh–Schrödinger term and the intra‐atomic correlation contribution to the second‐order component play a significant role. For intermediate and large distances (including the equilibrium distance), it is found that the perturbational expansion limited to the complete first‐ and second‐order, plus the third‐order Rayleigh–Schrödinger energy agrees with the best known values of the total interaction energy of the helium dimer.