The Dose Makes the Poison: Perturbative Steps Toward the Ultimate Linearized Coupled Cluster Method
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866914355278249984 |
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| author | Bintrim, Sylvia J. Ransford, Ella R. Carter-Fenk, Kevin |
| author_facet | Bintrim, Sylvia J. Ransford, Ella R. Carter-Fenk, Kevin |
| contents | "Addition-by-subtraction" coupled cluster (CC) approaches provide a promising approach to treating the difficult strong correlation problem by simplifying the standard CC equations. In a separate vein, linearized CC methods have drawn interest for their lower computational cost, increased parallelizability, and favorable properties for extension to the excited state--but the inclusion of ring/crossed-ring terms causes singularities even for single bond breaking. A linearized, addition-by-subtraction CC method called linearized ladder CCD (linLCCD) removes these terms to avoid divergences, but linLCCD under-estimates dynamical correlation. Herein we resolve this deficiency of linLCCD by introducing a linearized external coupled cluster perturbation theory that adds a second-order ring/crossed-ring correction back into a linLCCD reference wave function. Our resultant xlinCCD(2) method is regular and yields comparable results to linearized CCD in weakly-correlated regimes. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_02149 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Dose Makes the Poison: Perturbative Steps Toward the Ultimate Linearized Coupled Cluster Method Bintrim, Sylvia J. Ransford, Ella R. Carter-Fenk, Kevin Strongly Correlated Electrons "Addition-by-subtraction" coupled cluster (CC) approaches provide a promising approach to treating the difficult strong correlation problem by simplifying the standard CC equations. In a separate vein, linearized CC methods have drawn interest for their lower computational cost, increased parallelizability, and favorable properties for extension to the excited state--but the inclusion of ring/crossed-ring terms causes singularities even for single bond breaking. A linearized, addition-by-subtraction CC method called linearized ladder CCD (linLCCD) removes these terms to avoid divergences, but linLCCD under-estimates dynamical correlation. Herein we resolve this deficiency of linLCCD by introducing a linearized external coupled cluster perturbation theory that adds a second-order ring/crossed-ring correction back into a linLCCD reference wave function. Our resultant xlinCCD(2) method is regular and yields comparable results to linearized CCD in weakly-correlated regimes. |
| title | The Dose Makes the Poison: Perturbative Steps Toward the Ultimate Linearized Coupled Cluster Method |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2602.02149 |