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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2605.20556 |
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Table of Contents:
- The double electron attachment (DEA) and double ionization potential (DIP) equation-of-motion coupled-cluster (EOMCC) methods including up to 4-particle-2-hole (4$p$-2$h$) and 4-hole-2-particle (4$h$-2$p$) excitations on top of coupled-cluster singles, doubles, and triples (CCSDT), denoted DEA-EOMCCSDT(4$p$-2$h$) and DIP-EOMCCSDT(4$h$-2$p$), have been efficiently implemented in full and active-space forms. The resulting methods are applied to determine the ground and low-lying excited states of methylene, the singlet-triplet gap of trimethylenemethane, and the lowest singlet and triplet DIPs of 23 atoms and molecules. In all cases considered, the active-space DEA/DIP-EOMCC approaches recover the highly accurate parent DEA-EOMCCSDT(4$p$-2$h$)/DIP-EOMCCSDT(4$h$-2$p$) data at small fractions of the computational costs.