Modeling Electron Correlation Using Geminal Hybrid Methods

Two approaches to dynamic correlation correction for a variationally optimized, spin-unrestricted, multireference wavefunction based on strongly orthogonal, two electron geminals are presented. The first is a simple density functional based approach using standard correlation functionals rescaled empirically to reduce the correlation double counting error (DCE) inherent in all multireference DFT approaches. The second uses a two electron correlation operator to correlate only intergeminal, mean-field type, interactions within the wavefunction and effectively eliminates DCE. The performance of each is examined by geometric optimization and dissociation energy prediction of 38 diatomic molecules at two different basis sets.