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## Green’s function coupled cluster formulations utilizing extended inner excitations

## Abstract

Here, we analyze new approximations of the Green’s function coupled cluster (GFCC) method where locations of poles are improved by extending the excitation level of inner auxiliary operators. These new GFCC approximations can be categorized as the GFCC-i( *n, m*) method, where the excitation level of the inner auxiliary operators ( *m*) used to describe the ionization potential and electron affinity effects in the N-1 and N+1 particle spaces is higher than the excitation level ( *n*) used to correlate the ground-state coupled cluster wave function for the N-electron system. Furthermore, we reveal the so-called “n + 1” rule in this category [or the GFCC-i( *n, n* + 1) method], which states that in order to maintain size-extensivity of the Green’s function matrix elements, the excitation level of inner auxiliary operators X _{p}(ω) and Y _{q}(ω) cannot exceed *n* + 1. We also discuss the role of the moments of coupled cluster equations that in a natural way assures these properties. Our implementation in the present study is focused on the first approximation in this GFCC category, i.e., the GFCC-i(2,3) method. As our first practice, we use the GFCC-i(2,3) method to compute the spectral functions for the N _{2} andmore »

- Authors:

- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

- Publication Date:

- Research Org.:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)

- OSTI Identifier:
- 1489236

- Report Number(s):
- PNNL-SA-136088

Journal ID: ISSN 0021-9606

- Grant/Contract Number:
- AC05-76RL01830

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of Chemical Physics

- Additional Journal Information:
- Journal Volume: 149; Journal Issue: 21; Journal ID: ISSN 0021-9606

- Publisher:
- American Institute of Physics (AIP)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ab initio; coupled cluster calculations; Coupled cluster Green function

### Citation Formats

```
Peng, Bo, and Kowalski, Karol. Green’s function coupled cluster formulations utilizing extended inner excitations. United States: N. p., 2018.
Web. doi:10.1063/1.5046529.
```

```
Peng, Bo, & Kowalski, Karol. Green’s function coupled cluster formulations utilizing extended inner excitations. United States. doi:10.1063/1.5046529.
```

```
Peng, Bo, and Kowalski, Karol. Wed .
"Green’s function coupled cluster formulations utilizing extended inner excitations". United States. doi:10.1063/1.5046529.
```

```
@article{osti_1489236,
```

title = {Green’s function coupled cluster formulations utilizing extended inner excitations},

author = {Peng, Bo and Kowalski, Karol},

abstractNote = {Here, we analyze new approximations of the Green’s function coupled cluster (GFCC) method where locations of poles are improved by extending the excitation level of inner auxiliary operators. These new GFCC approximations can be categorized as the GFCC-i(n, m) method, where the excitation level of the inner auxiliary operators (m) used to describe the ionization potential and electron affinity effects in the N-1 and N+1 particle spaces is higher than the excitation level (n) used to correlate the ground-state coupled cluster wave function for the N-electron system. Furthermore, we reveal the so-called “n + 1” rule in this category [or the GFCC-i(n, n + 1) method], which states that in order to maintain size-extensivity of the Green’s function matrix elements, the excitation level of inner auxiliary operators Xp(ω) and Yq(ω) cannot exceed n + 1. We also discuss the role of the moments of coupled cluster equations that in a natural way assures these properties. Our implementation in the present study is focused on the first approximation in this GFCC category, i.e., the GFCC-i(2,3) method. As our first practice, we use the GFCC-i(2,3) method to compute the spectral functions for the N2 and CO molecules in the inner and outer valence regimes. Lastly, in comparison with the Green’s function coupled cluster singles, doubles results, the computed spectral functions from the GFCC-i(2,3) method exhibit better agreement with the experimental results and other theoretical results, particularly in terms of providing higher resolution of satellite peaks and more accurate relative positions of these satellite peaks with respect to the main peak positions.},

doi = {10.1063/1.5046529},

journal = {Journal of Chemical Physics},

number = 21,

volume = 149,

place = {United States},

year = {2018},

month = {12}

}

Works referenced in this record:

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