Orbital energy using Slater double-zeta functions

In the 1960s, this last statement was not acceptable and, indeed, it was to minimize such discrepancies that prompted Clementi to propose his optimized double-zeta sets. That better results can be obtained using this approach is shown in Figure 1.12, wherein the comparisons are made between the optimized Clementi double-zeta function and the numerical results. The detail of this calculation requires the involvement of the variation principle to determine the relative weightings of the two components of the double-zeta basis by minimizing the calculated 2s orbital energy. This requires that the 2s function be rendered orthonormal [Chapters] to the Is function in lithium. Thus, all four Slater functions in the Clementi double-zeta basis, the two for the 1 s and the two for the 2s, contribute to... 

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