Explicitly correlated Gaussian functions with r 122n factors for calculations of the ground state of the helium atom

Explicitly correlated Gaussian functions with r 122n exp( − βr 122) factors have been used in variational calculations of the ground state of the helium atom. Additional correlation factors in the form of even powers of r_ij were introduced to the Gaussian functions with exponential correlation components by differentiating these functions with respect to the correlation exponent β. The algorithm of this method and its computational implementation is described. A number of calculations were performed for the ground state of helium atom to test the performance of the basis sets comparising different numbers of the Gaussians with the exp( − βr 122) and r 122 exp( − βr 122) correlation factors. The numerical results indicate that including functions with r 122 factors does not lead to improved results, contrary to what was anticipated initially. © 1994 by John Wiley & Sons, Inc.