Slide 11 of 17
GVB-LMP2 performs multireference perturbation calculations. The approach is based on a GVB formulation of the underlying MC-SCF reference wavefunction with LMP2 supplying the perturbative corrections.
Methods of comparable level of theory, QCISD(T), for example, are far more expensive, and may scale as much as N7 with basis set size. Jaguar‘s GVB-LMP2, however, employs the pseudospectral methods to enhance the performance of both components, thus enabling highly correlated calculations at a fraction of the cost, at roughly N3.
The importance of using a multiconfigurational reference has been demonstrated in a study of relative conformational energies including 36 molecules. The GVB-LMP2 results show uniform agreement with experiments, with an MAD (Mean absolute deviation) of 0.19 kcal/mole, and an absolute RMS deviation of 0.23 kcal/mole. The multireference approach is shown to be necessary to correctly represent the low lying pi excitations of the carbon-carbon double bonds.
Similarly, multireference character will likely play a significant role in the accurate description of transition states and systems containing transition metals.