A new functional for variational calculation of atomic and molecular second-order correlation energies

Second-order correlation energies for atoms and molecules are calculated with a novel variational functional that is closely related to the one used before but neglects the most time-consuming terms. Consequently much larger basis sets could be used. Results for He, Be, H₂ and LiH obtained with an explicitly correlated gaussian geminal basis are better than the best published results by 0.32, 0.06, 3.3, and 6.2% and are estimated to be accurate to within a fraction of 1%.