Coupled cluster singles and doubles CCSD

The geometry has been optimized at HF, B-LYP, and MP2 levels with the 3-21G basis set on these geometries, single-point energy values have been computed at MP4 and coupled-cluster singles and doubles (CCSD) levels (Table 7) <1998SM(92)69>. 

In this section we construct working equations for the coupled cluster singles and doubles (CCSD) method. Beginning from the approximation 7 = 7 + T2, we use algebraic and diagrammatic techniques to obtain programmable... 

H. Koch, O. Christiansen, R. Kobayashi, P. Jorgensen, and T. Helgaker, Chem. Phys. Lett., 228, 233 (1994). A Direct Atomic Orbital Driven Implementation of the Coupled Cluster Singles and Doubles (CCSD) Model. 

For higher fluoro derivatives, namely di- and 1,2,3-trifluoro derivatives we have also employed the coupled-clusters singles and doubles (CCSD) method with TZ2P... 

In this coupled-cluster singles and doubles (CCSD) approximation, none of the coefficients in the FCI expansion is ignored. Instead, they are approximated by a much smaller set of singles and doubles amplitudes. 

Analytic Energy Gradients for Open-Shell Coupled-Cluster Singles and Doubles (CCSD) Calculations Using Restricted Open-Shell Hartree-Fock (ROHF) Reference Functions. 

SM calculations are broadly based on either the (i) Hartree-Fock method (ii) Post-Hartree-Fock methods like the Mpller-Plesset level of theory (MP), configuration interaction (Cl), complete active space self-consistent field (CASSCF), coupled cluster singles and doubles (CCSD) or (iii) methods based on DFT [24-27]. Since the inclusion of electron correlation is vital to obtain an accurate description of nearly all the calculated properties, it is desirable that SM calculations are carried out at either the second-order Mpller-Plesset (MP2) or the coupled cluster with single, double, and perturbative triple substitutions (CCSD(T)) levels using basis sets composed of both diffuse and polarization functions. 

CASPT2 complete aetive spaee based second-order perturbation theory CCSD coupled-cluster single and double CCSD(T) CCSD corrected with triple excitations Cl configmation interaction... 

Coupled cluster theory Coupled cluster theory has been employed for calculations of the spin-spin coupling constants by Perera, Sekino and Bartlett 52.53 They have derived the indirect spin-spin coupling constant as a derivative of the coupled cluster singles and doubles (CCSD) energy (see... 

The coupled cluster method is the Cl method based on this wavefunction. One of the noain advantages of this method is to ensure size consistency (see Sect. 3.3) in the selection of electron configurations. In coupled cluster methods, the coupled-cluster singles and doubles (CCSD) method terminates f up to the double excitation... 

The purpose of the present work is to test the efficiency and performance of the implementation of the explicitly correlated coupled-cluster singles-and-doubles, CCSD(F12), model in the Turbomole package. This model, initially proposed by Fliegl et al. [41], is the approximation to the full CCSD-F12 approach originally given by Noga et al [40]. It has been demonstrated that this method is able to recover quintuple- quality correlation energies with the orbital basis set of the size of triple- [31]. 

The PCM coupled-cluster theory has been presented at the coupled-cluster single and double (CCSD) excitation level approximation [9, 11], at the Brueckner doubles (BD) coupled-cluster level [12], and within the symmetry adapted cluster (SAC) method [10]. 

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