We have recently formulated a nonperturbative version of the multireference driven similarity renormalization group (MR-DSRG) approach, where all operators are truncated to contain at most two-body terms [1]. The resulting MR-LDSRG(2) theory yields highly accurate potential energy curves for single-bond dissociation processes [2]. This accuracy deteriorates for multiple-bond dissociations like, for example, the triple bond in N<sub>2</sub>. Here, we attempt to solve the problem by correcting the MR-LDSRG(2) truncation scheme for three-body correlations. We perform a generalized perturbative analysis [3] of the MR-DSRG to evaluate the importance of triples and correct the Hamiltonian for missing fourth-order terms. In addition we consider extensions of the formalism to a recently introduced state-averaged approach [4].<br/><br/>

Perturbative triples corrections in the multireference driven similarity renormalization group

2019 Spring National Meeting

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