Higher dispersion coefficients for the interaction of helium atoms

The odd-order dispersion coefficients C 11 , C 13 , C 15 appearing in the third order of perturbation theory, and the even-order ones C 12 , C 14 , C 16 with contributions from the second and fourth order were calculated for binary interactions among helium atoms in the lowest singlet and triplet S states. The computations were carried out in the determinant based full configuration interaction approach using specially optimized Gaussian basis sets. The sum-over-pseudostates technique was employed to construct the reduced resolvent. The results of our calculations show a limited accuracy of the extrapolation formulas used thus far to compute these higher-order coefficients.