2022
DOI: 10.1021/acs.jctc.1c01099
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Second-Order Active-Space Embedding Theory

Abstract: Quantum embedding schemes are a promising way to extend multireference computations to large molecules with strong correlation effects localized on a small number of atoms. This work introduces a second-order active-space embedding theory [ASET(2)] which improves upon mean-field frozen embedding by treating fragment−environment interactions via an approximate canonical transformation. The canonical transformation employed in ASET(2) is formulated using the driven similarity renormalization group. The ASET(2) s… Show more

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Cited by 13 publications
(8 citation statements)
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“…The computational problem of treating a small "active space" of correlated defect states within a relatively weakly correlated bulk (i.e., supercell or cluster) is thus ideal for a quantum embedding approach [20,21]. Such approaches have enjoyed extensive success in quan-tum chemistry [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] and solid-state physics [20,[38][39][40] for treating strongly correlated materials and molecules. Recently, their popularity for treating defects [41][42][43][44][45][46] and other inhomogeneous systems [47][48][49][50][51][52][53][54][55] has increased rapidly.…”
Section: Introductionmentioning
confidence: 99%
“…The computational problem of treating a small "active space" of correlated defect states within a relatively weakly correlated bulk (i.e., supercell or cluster) is thus ideal for a quantum embedding approach [20,21]. Such approaches have enjoyed extensive success in quan-tum chemistry [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] and solid-state physics [20,[38][39][40] for treating strongly correlated materials and molecules. Recently, their popularity for treating defects [41][42][43][44][45][46] and other inhomogeneous systems [47][48][49][50][51][52][53][54][55] has increased rapidly.…”
Section: Introductionmentioning
confidence: 99%
“…After generating CASSCF orbitals, we apply the mean-field version of ASET [ASET­(mf)] . The ASET­(mf) scheme is used to localize and separate orbitals into two sets: fragment (A) and environment (B) orbitals. , This step requires the user to specify a list of atoms assigned to the fragment. To accurately reproduce the interaction of CO with the surface, the fragment space should contain the orbitals of CO and the closest Na and Cl atoms.…”
Section: Theorymentioning
confidence: 99%
“…The mean-field version of ASET accounts for the fragment–environment interaction with a static effective one-electron potential. Although this treatment neglects instantaneous fragment–environment fluctuations, a study that introduced this missing effect at the second-order level in perturbation theory found only a small improvement in the energetics . The present embedding method is well suited for insulator surfaces.…”
Section: Theorymentioning
confidence: 99%
“…In this section, we provide a synopsis of the SA-DSRG formalism and rationalize the accuracy of various approximate methods. Curious readers are referred to refs and for detailed derivations and refs and for a broader perspective of DSRG. We begin with an ensemble of CASCI states double-struckE 0 { Ψ α | α = 1, 2 , ... , n } obtained from a SA CAS self-consistent-field (CASSCF) computation .…”
Section: Theorymentioning
confidence: 99%