Basis set dependent SCα exchange-only and exchange-correlation calculations

Abstract

The SCα method [V. V. Karasiev and E.V. Ludeña, Phys. Rev. A 65, 062510 (2002)], has been implemented into a local version of the GAUSSIAN 98 program package. Using this modified code we have calculated total energies of selected atoms and molecules belonging to the G2 set within the KS-exchange-only and KS-exchange-correlation approximations. In these calculations we have used the exchange functionals LDA, B1, and PW91 and their SCα counterparts: SCα-LDA, SCα-B1, and SCα-PW91. The corresponding exchange-correlation functionals are B3LYP and SCα-B3LYP. We have also explored the basis set dependence of the SCα method by calculating the KS-exchange-only atomization energies using the following hierarchy of basis set functions: STO-3G, 6-31G*, 6-31G**, and 6-311++G(3df,3pd). The average error values of the SCα calculations (with respect to exact exchange EXX values) are 121, 133, and 128 kJ mol−1 (for the SCα-LDA, SCα-PW91, and SCα-B1 methods, respectively) for the STO-3G basis set; 20, 27, and 19 kJ mol−1 (for the SCα-LDA, SCα-PW91, and SCα-B1 functionals) for the 6-31G**; and 7, 10, 5 kJ mol−1, respectively, for the 6-311++G(3df,3pd). Hence, it is seen that the application of the SCα method to LDA, B1, and PW91 exchange functionals, yields atomization energies in close agreement with the EXX ones as long as a large enough basis set is used. Moreover, the SCα atomization energies calculations performed using the modified GAUSSIAN 98 code (for the spin unrestricted case), are much closer to the EXX values than those obtained using a spin-restricted numerical code.