Breaking Bonds of Open-Shell Species with the Restricted Open-Shell Size Extensive Left Eigenstate Completely Renormalized Coupled-Cluster Method

Abstract

The recently developed restricted open-shell, size extensive, left eigenstate, completely renormalized (CR), coupled-cluster (CC) singles (S), doubles (D), and noniterative triples (T) approach, termed CR-CC(2,3) and abbreviated in this paper as ROCCL, is compared with the unrestricted CCSD(T) [UCCSD(T)] and multireference second-order perturbation theory (MRMP2) methods to assess the accuracy of the calculated potential energy surfaces (PESs) of eight single bond-breaking reactions of open-shell species that consist of C, H, Si, and Cl; these types of reactions are interesting because they account for part of the gas-phase chemistry in the silicon carbide chemical vapor deposition. The full configuration interaction (FCI) and multireference configuration interaction with Davidson quadruples correction [MRCI(Q)] methods are used as benchmark methods to evaluate the accuracy of the ROCCL, UCCSD(T), and MRMP2 PESs. The ROCCL PESs are found to be in reasonable agreement with the corresponding FCI or MRCI(Q) PESs in the entire region R = 1−3Re for all of the studied bond-breaking reactions. The ROCCL PESs have smaller nonparallelity error (NPE) than the UCCSD(T) ones and are comparable to those obtained with MRMP2. Both the ROCCL and UCCSD(T) PESs have significantly smaller reaction energy errors (REE) than the MRMP2 ones. Finally, an efficient strategy is proposed to estimate the ROCCL/cc-pVTZ PESs using an additivity approximation for basis set effects and correlation corrections. The recently developed restricted open-shell, size extensive, left eigenstate, completely renormalized (CR), coupled-cluster (CC) singles (S), doubles (D), and noniterative triples (T) approach, termed CR-CC(2,3) and abbreviated in this paper as ROCCL, is compared with the unrestricted CCSD(T) [UCCSD(T)] and multireference second-order perturbation theory (MRMP2) methods to assess the accuracy of the calculated potential energy surfaces (PESs) of eight single bond-breaking reactions of open-shell species that consist of C, H, Si, and Cl; these types of reactions are interesting because they account for part of the gas-phase chemistry in the silicon carbide chemical vapor deposition. The full configuration interaction (FCI) and multireference configuration interaction with Davidson quadruples correction [MRCI(Q)] methods are used as benchmark methods to evaluate the accuracy of the ROCCL, UCCSD(T), and MRMP2 PESs. The ROCCL PESs are found to be in reasonable agreement with the corresponding FCI or MRCI(Q) PESs in the entire region R ) 1-3R e for all of the studied bond-breaking reactions. The ROCCL PESs have smaller nonparallelity error (NPE) than the UCCSD(T) ones and are comparable to those obtained with MRMP2. Both the ROCCL and UCCSD(T) PESs have significantly smaller reaction energy errors (REE) than the MRMP2 ones. Finally, an efficient strategy is proposed to estimate the ROCCL/cc-pVTZ PESs using an additivity approximation for basis set effects and correlation corrections.

Progress and Challenges in the Calculation of Electronic Excited States

“…[33] Large improvements in the CC description of multiconfigurational and degenerate situations have been reached with the completely renormalized coupled-cluster (CR-CC) approach, whose use needs to be generalized. [43] Multireference coupledcluster (MRCC) methods have been a long-time promise of accuracy and generality that has not been completely fulfilled, although there have been many attempts to develop efficient algorithms. [44] …”

Extension of coupled-cluster theory with a noniterative treatment of connected triply excited clusters to three-body Hamiltonians

“…(67) and (68). As a result, the CR-CC(2,3) correction δE (T) , which offers an accurate representation of the T 3 effects on the correlation energy without forcing one to solve for T 3 using the full CCSDT approach, assumes the following compact form: …”

Evaluation of density functional methods on the geometric and energetic descriptions of species involved in Cu+-promoted catalysis

“…Therefore, the electron correlation effects missed by MP2 within a given basis set may be safely assumed to be properly estimated by forming the difference of the CCSD(T) and MP2 energies determined using a smaller basis set. Thus, in addition to the pure CCSD(T)/cc-pVDZ results, we have performed "composite" calculations [57], in which the energy is defined as MP2/(augcc-pVTZ + SBKJ) + [CCSD(T) -MP2]/(cc-pVDZ + SBKJ). In this case, the majority of the electron correlation is described using the aug-cc-pVTZ basis set and the smaller missing electron correlation (3-5 %) using the cc-pVDZ basis.…”