EOM-CC Methods with Approximate Triple Excitations for NEXAFS and XPS
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arXiv
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| Formato: | Preprint |
| Publicado: |
2020
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| _version_ | 1866910890375249920 |
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| author | Matthews, Devin A. |
| author_facet | Matthews, Devin A. |
| contents | A number of iterative and perturbative approximations to the full equation-of-motion coupled cluster method with single, double, and triple excitations (EOM-CCSDT) are evaluated in the context of calculating the K-edge core-excitation and core-ionization energies of several small molecules. Several of these methods are found to accurately reproduce the full EOM-CCSDT energies well, in particular the EOM-CCSD* method which, when using the core-valence separation (CVS) ansatz, scales rigorously with the sixth power of molecular size. The EOM-CCSDR(3) method, which has been used previously to include triples effects in a cost-effective manner was found to perform rather poorly, although the precise cause has not been determined. These results highlight that very accurate NEXAFS and XPS spectra for molecules with first-row atoms can be computed at a cost not much larger than that for EOM-CCSD. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2001_09218 |
| institution | arXiv |
| publishDate | 2020 |
| record_format | arxiv |
| spellingShingle | EOM-CC Methods with Approximate Triple Excitations for NEXAFS and XPS Matthews, Devin A. Chemical Physics A number of iterative and perturbative approximations to the full equation-of-motion coupled cluster method with single, double, and triple excitations (EOM-CCSDT) are evaluated in the context of calculating the K-edge core-excitation and core-ionization energies of several small molecules. Several of these methods are found to accurately reproduce the full EOM-CCSDT energies well, in particular the EOM-CCSD* method which, when using the core-valence separation (CVS) ansatz, scales rigorously with the sixth power of molecular size. The EOM-CCSDR(3) method, which has been used previously to include triples effects in a cost-effective manner was found to perform rather poorly, although the precise cause has not been determined. These results highlight that very accurate NEXAFS and XPS spectra for molecules with first-row atoms can be computed at a cost not much larger than that for EOM-CCSD. |
| title | EOM-CC Methods with Approximate Triple Excitations for NEXAFS and XPS |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2001.09218 |