Comparison of MBPT and coupled-cluster methods with full CI. Importance of triplet excitation and infinite summations |
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| Authors: | Rodney J Barlett Hideo Sekino George D Purvis |
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| Institution: | Quantum Theory Project, Departments of Chemistry and Physics, University of Florida, Gainesville, Florida 32611 USA |
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| Abstract: | Results from full fourth-order perturbation theory SDTQ MBPT(4)], and the coupled-cluster single- and double-excitation model (CCSD). are compared with recent full CI results for BH, HF, NH3, and H2O. For H2O, studies include large symmetric displacements of the OH bonds, which offer a severe test for any single-reference MBPT/CC method. In every case. CCSD plus fourth-order triple-excitation terms provide agreement with the full CI to < 2 kcal/mole. SDTQ MBPT(4) has an error 10 kcal/mole for displaced H2O. |
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