Fock-Space Coupled Cluster Theory: Systematic Study of Partial Fourth Order Triples Schemes for Ionization Potential and Comparison with Bondonic Formalism

Abstract

In this paper, we have made a systematic study of partial fourth order perturbative schemes due to triples to compute the ionization potential within Fock-space multi-reference coupled-cluster theory. In particular, we have obtained computationally less expensive correlation schemes due to fourth order triples. Prototype examples have been considered to explore the efficacy of the approximate methods mentioned, while the bondonic formalism supporting the bonding phenomenology is also respectively for the first time here advanced.

Three-Body Excitations in Fock-Space Coupled-Cluster: Fourth Order Perturbation Correction to Electron Affinity and Its Relation to Bondonic Formalism

“…Quite recently, the bondonic formalism provided an alternative formal way of describing the fourth-order perturbation treatment of the ionization potentials of molecules, by advancing the N-body k-order of interaction of bondonic contribution to the specific contraction [71], as follows:…”

“…N-the total number of electrons in the bonding state of matter (it can be either ground state or valence state, or another involved in chemical reactivity); k-the perturbation order; l-the total number of loops over all the diagrams involved [71,82].…”

“…Within the intermediate Hamiltonian version, the work of Musial and co-workers, in the inclusion of triples, should also be mentioned [70]. However, compared to all these developments, the novel aspect of the work that is presented here is the partial fourth-order schemes, which have only been attempted recently by us [71], in the context of IP calculations; with that occasion, the bondonic formalism was also illustrated for the first time, for treating such higher-order perturbation excitation effects.…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…This direction is represented by 39 articles [ 28 , 35 , 129 , 134 , 136 , 190 , 191 , 192 , 193 , 194 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 208 , 209 , 210 , 211 , 212 , 213 , 214 , 215 , 216 , 217 , 218 , 219 , 220 , 221 , 222 , 223 ]. Their distribution, according to the above types, is presented in Table 7 .…”

Resonance study: Effect of partial triples excitation using complex absorbing potential‐based Fock‐space multi‐reference coupled cluster

“…FSMRCC with singles and doubles approximations has been used very effectively for the calculation of difference energies [29][30][31]. However, to get more accurate spectroscopic energies partial [32][33][34][35] and full triples were implemented [36,37]. Full triples are too expensive and hence partial inclusion of triples is more desirable.…”