Fast geometry optimizations with RI-SCF based gradients

If geometry optimizations on MP2 or CC2 level are performed with large basis set, especially with diffuse basis functions, the N⁴-steps might become the dominant part of the overall timings. In these cases, the integral screening in the Hartree-Fock part often becomes inefficient. The resolution-of-the-identity can be applied here to speed up the calculation of the HF reference wavefunction, as well as the solution of the coupled-perturbed Hartree-Fock (CPHF) equations in the MP2 or CC2 gradient calculation.

An additional auxiliary basis (denoted jkbas) set has to be assigned via the General Options Menu in the define program. In the submenu rijk choose on and select your auxiliary basis set. Then, run the jobex script the additional rijk-flag:

> jobex -level cc2 -rijk

Note, that it is at the moment not possible to perform these calculation parallel because the RI-JK approximation is presently not supported in the parallel version of the ridft program.