The successful computational cost speedups of the previous sections often leave
the cost of the underlying SCF calculation dominant. The dual-basis method
provides a means of accelerating the SCF by roughly an order of magnitude, with
minimal associated error (see Section 4.7). This dual-basis
reference energy may be combined with RI-MP2 calculations for both
J. Chem. Phys.
(2006), 125, pp. 074108. , 1137 J. Chem. Theory Comput.
(2009), 5, pp. 1560. and analytic first derivatives. 288 Mol. Phys.
(2007), 105, pp. 2731. In the latter case, further savings (beyond the SCF alone) are demonstrated in the gradient due to the ability to solve the response (-vector) equations in the smaller basis set. Refer to Section 4.7 for details and job control options.