Single-root multireference Brillouin-Wigner coupled-cluster theory: Applicability to the F2 molecule

Abstract

Articles you may be interested inBlock correlated coupled cluster theory with a complete active-space self-consistent-field reference function: The formulation and test applications for single bond breaking On the ground states of CaC and ZnC: A multireference Brillouin-Wigner coupled cluster study J. Chem. Phys. 117, 9733 (2002); 10.1063/1.1516809 Brillouin-Wigner coupled cluster theory. Fock-space approachRecently developed single-root multireference Brillouin-Wigner coupled-cluster ͑MR BWCC͒ theory, which deals with one state at a time while employing a multiconfigurational reference wave function, is applied to the ground state of the F 2 molecule using a two-determinant reference space at the level of the CCSD approximation. The method represents a brand-new coupled-cluster ͑CC͒ approach to quasidegenerate problems which combines merits of two theories: the single-reference CC method in a nondegenerate case and the Hilbert space MR CC method in quasidegenerate case. The method is able to switch itself from a nondegenerate to a fully degenerate case in a continuous manner, providing thus smooth potential energy surfaces. Moreover, in contrast to the Hilbert space MR CC approaches, it does not contain the so-called coupling terms and completely reduces to the standard single-reference CC method in a highly nondegenerate region. Using a ͓4s,3p,1d͔ and ͓4s,3p,2d,1f ͔ basis sets, the calculated potential energy curves are smooth, dissociate correctly and the results are compared with other available multireference techniques as well as experiment.

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

“…To avoid the intruder states, the SS-MRCC approach [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103], which treats one state at a time with a state-specific wave operator, has been developed. Existing SS-MRCC methods include, for example, Mk-CCSD [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95], single-root MR BWCCSD [96][97][98][99][100][101], and MRexpT [102,103]. These methods have been shown to give quite accurate descriptions for electronic structures of molecules with strong multireference character.…”

Electronic structure of organic diradicals: Evaluation of the performance of coupled-cluster methods

“…Following Ref 19,. The third possible approach relies on the Brillouin-Wigner ͑BW͒ form of MR CC equations[61][62][63][64][65][66][67][68] This approach was recently implemented in general purpose codes by Evangelista et al59,60 and applied to a number of systems, including diradicaloid species.…”

Accurate ab initio potential energy curve of F2. I. Nonrelativistic full valence configuration interaction energies using the correlation energy extrapolation by intrinsic scaling method

“…Its rovibrational ground state spectrum has been accurately determined by experiment, 108,109 which allows the critical assessment of the theoretical results in all regions of the dissociation curve. While there exist numerous investigations of the nearequilibrium properties [110][111][112][113][114][115][116][117][118] and some theoretical studies of the dissociation curve, 66,68,69,71,[119][120][121][122][123][124][125][126][127][128][129] the latter has proven to be a difficult case due to the weakness of its chemical bond. 130 As yet, no attempt has been made to obtain the full potential energy curve with an accuracy that would warrant calculating the full vibration rotation spectrum.…”