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The f-block ab initio correlation consistent composite approach was used to predict the dissociation energies of lanthanide sulfides and selenides. Geometry optimizations were carried out using density functional theory and coupled cluster singles, doubles, and perturbative triples with one- and two-component Hamiltonians. For the two-component calculations, relativistic effects were accounted for by utilizing a third-order Douglas–Kroll–Hess Hamiltonian. Spin–orbit coupling was addressed with the Breit–Pauli Hamiltonian within a multireference configuration interaction approach. The state averaged complete active space self-consistent field wavefunctions obtained for the spin–orbit coupling energies were used to assign the ground states of diatomics, and several diagnostics were used to ascertain the multireference character of the molecules.
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This content will become publicly available on March 14, 2026
Revealing correlation mechanisms through nonorthogonal multiconfiguration self-consistent field calculations
The presence of spin and spatial symmetry breaking upon variational optimization of mean-field wavefunctions is known to be an indicator of nondynamical electron correlation. However, a single mean-field wavefunction may not have sufficient flexibility to flag the correlated orbital space where there are multiple correlation mechanisms present. In such situations, there are multiple nearly degenerate self-consistent field solutions that describe different correlation mechanisms, but it is often not possible to know a priori when such situations will occur or if sufficient solutions have been obtained. In this work, we examine the role of spin and spatial symmetries of nonorthogonal multiconfigurational self-consistent field (NOMCSCF) calculations in revealing correlation mechanisms. We provide details of the theory for optimization of NOMCSCF wavefunctions with desired symmetries, establish which types of symmetries recover the most correlation energy when the symmetry constraints are relaxed, and discuss how the different-orbitals for different-configuration wavefunctions reveal the different correlation mechanisms present.
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- Award ID(s):
- 2144905
- PAR ID:
- 10579594
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 162
- Issue:
- 10
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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