We present some systematic calculations of dynamic multipole polarizabilities and van der Waals dispersion coefficients for the helium atom and ${\mathrm{H}}_2$ molecule with a quantum Monte Carlo calculation. Using an original method based on a gauge-invariant formalism we also report some ab nitio results of the same quantities. In light of the results we discuss the advantages and drawbacks of both approaches in comparison to prior theoretical results.

• Received 14 September 1992

DOI:https://doi.org/10.1103/PhysRevA.47.3704