Reduced-Cost Four-Component Relativistic Double Ionization Potential Equation-of-Motion Coupled-Cluster Approaches with 4-Hole--2-Particle Excitations and Three-Body Clusters
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2025
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| _version_ | 1866914044817965056 |
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| author | Mukhopadhyay, Tamoghna Mukherjee, Madhubani Gururangan, Karthik Piecuch, Piotr Dutta, Achintya Kumar |
| author_facet | Mukhopadhyay, Tamoghna Mukherjee, Madhubani Gururangan, Karthik Piecuch, Piotr Dutta, Achintya Kumar |
| contents | The double ionization potential (DIP) equation-of-motion (EOM) coupled-cluster (CC) method with 4-hole--2-particle (4$h$-2$p$) excitations on top of the CC with singles, doubles, and triples calculation, abbreviated as DIP-EOMCCSDT(4$h$-2$p$), along with its perturbative DIP-EOMCCSD(T)(a)(4$h$-2$p$) approximation, are extended to a relativistic four-component (4c) framework. In addition, we introduce and test a new computationally practical DIP-EOMCC approach, which we call DIP-EOMCCSD(T)($\tilde{a}$)(4$h$-2$p$), that approximates the treatment of 4$h$-2$p$ correlations within the DIP-EOMCCSD(T)(a) (4$h$-2$p$) method and reduces the $\mathscr{N}^8$ scaling characterizing DIP-EOMCCSDT(4$h$-2$p$) and DIP-EOMCCSD(T)(a)(4$h$-2$p$) to $\mathscr{N}^7$ with the system size $\mathscr{N}$. Further improvements in computational efficiency are obtained using the frozen natural spinor (FNS) approximation to reduce the numbers of unoccupied spinors entering the correlated steps of the DIP-EOMCC calculations according to a well-defined occupation-number-based threshold. The resulting 4c-FNS-DIP-EOMCC approaches are used to compute DIPs for the series of inert gas atoms from argon to radon as well as the vertical DIPs in \Cltwo{}, \Brtwo{}, HBr, and HI, which have been experimentally examined in the past. We demonstrate that, when using complete basis set extrapolations and FNS truncation thresholds of $10^{-4.5}$, the 4c-FNS-DIP-EOMCCSD(T)($\tilde{a}$)(4$h$-2$p$) calculations are capable of predicting DIPs in agreement with experimental data, improving upon their nonrelativistic and spin-free scalar-relativistic counterparts, particularly when examining DIPs characterized by stronger spin-orbit coupling effects. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_14779 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Reduced-Cost Four-Component Relativistic Double Ionization Potential Equation-of-Motion Coupled-Cluster Approaches with 4-Hole--2-Particle Excitations and Three-Body Clusters Mukhopadhyay, Tamoghna Mukherjee, Madhubani Gururangan, Karthik Piecuch, Piotr Dutta, Achintya Kumar Chemical Physics The double ionization potential (DIP) equation-of-motion (EOM) coupled-cluster (CC) method with 4-hole--2-particle (4$h$-2$p$) excitations on top of the CC with singles, doubles, and triples calculation, abbreviated as DIP-EOMCCSDT(4$h$-2$p$), along with its perturbative DIP-EOMCCSD(T)(a)(4$h$-2$p$) approximation, are extended to a relativistic four-component (4c) framework. In addition, we introduce and test a new computationally practical DIP-EOMCC approach, which we call DIP-EOMCCSD(T)($\tilde{a}$)(4$h$-2$p$), that approximates the treatment of 4$h$-2$p$ correlations within the DIP-EOMCCSD(T)(a) (4$h$-2$p$) method and reduces the $\mathscr{N}^8$ scaling characterizing DIP-EOMCCSDT(4$h$-2$p$) and DIP-EOMCCSD(T)(a)(4$h$-2$p$) to $\mathscr{N}^7$ with the system size $\mathscr{N}$. Further improvements in computational efficiency are obtained using the frozen natural spinor (FNS) approximation to reduce the numbers of unoccupied spinors entering the correlated steps of the DIP-EOMCC calculations according to a well-defined occupation-number-based threshold. The resulting 4c-FNS-DIP-EOMCC approaches are used to compute DIPs for the series of inert gas atoms from argon to radon as well as the vertical DIPs in \Cltwo{}, \Brtwo{}, HBr, and HI, which have been experimentally examined in the past. We demonstrate that, when using complete basis set extrapolations and FNS truncation thresholds of $10^{-4.5}$, the 4c-FNS-DIP-EOMCCSD(T)($\tilde{a}$)(4$h$-2$p$) calculations are capable of predicting DIPs in agreement with experimental data, improving upon their nonrelativistic and spin-free scalar-relativistic counterparts, particularly when examining DIPs characterized by stronger spin-orbit coupling effects. |
| title | Reduced-Cost Four-Component Relativistic Double Ionization Potential Equation-of-Motion Coupled-Cluster Approaches with 4-Hole--2-Particle Excitations and Three-Body Clusters |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2509.14779 |