RI-MP2 Calculations

The Resolution-of-the-identity Møller-Plesset second-order perturbation theory (RI-MP2) method [305–308] (also known as density-fitted MP2) method uses a linear combination of auxiliary basis functions to approximate electron densities in the two-electron integral calculations. This approach can closely reproduce canonical MP2 [93] energies at a reduced computational cost. Using RI-MP2 along with an SCF wavefunction evaluated with the Pseudospectral method further increases computational efficiency. The implementation of RI-MP2 is described in Pseudospectral Resolution-of-the-identity MP2 Techniques.

You can perform RI-MP2 single point energy computations and geometry optimizations for both open-shell and closed-shell systems. If you need other properties, such as frequencies and excitation energies, please use the DFT method.

The RI-MP2 method requires the use of auxiliary basis sets. By default, Jaguar selects an auxiliary basis set which corresponds to the basis set specified in the Input Tab of the Jaguar Panel. A warning message is displayed if you choose a basis set which cannot be used with the auxiliary basis sets found in Jaguar. You can also specify an auxiliary basis set with the keyword rimp2_auxbas. Available auxiliary basis sets are listed here.

By default, Jaguar's RI-MP2 implementation applies Spin-Component Scaled (SCS) MP2 304, where the correlation energy is separated into same-spin and opposite spin components, and scaling factors are separately applied to each component. This method has been shown to improve the accuracy of MP2 energies. If you do not want to calculate RI-SCS-MP2 energies but only RI-MP2 energies, you can set the same-spin (scs_os) and opposite-spin (scs_os) scaling factors to 1.1 Keywords scs_os and scs_ss in the gen section.