Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

SDQ-MBPT

SDQ-MBPT(4) results using 6s5p4d/5s3p basis of Bartlett et al. [107]. [Pg.73]

This simple reaction has significant interest because accurate experimental energy barrier data as well as the relative energy between the two minima are available [338]. For this reason different previous theoretical works have been performed at different levels of theory (HFS [20], SDQ-MBPT [38] and HF [39]). [Pg.265]

Our result is also in agreement with all other previous theoretical data. The experimental barrier is 38.4 kcal/mol [38]. We obtain 37.6 kcal/mol without zero point energy corrections. HF result overestimates the barrier by approximately 10 kcal/mol and the introduction of the correlation through the SDQ-MBPT(4) method reduces the overestimation by only 2.8 kcal/mol. The best agreement is found with the HFS result [20]. The TS geometry (see Figure 4) gives, as in the previous... [Pg.265]

The SDQ-MBPT(4) method, which includes all terms except the triple excitations, requires only an n N algorithm compared to n N N-,t (Nj = number of iterations) for CISDT. Allowing for its nonvariational character, it is generally better than CISDT (Table 2) because it has already incorporated most of the effects of quadruple excitations. Full MBPT(4) also benefits from the effect of triple excitations, is a noniterative —n N procedure, and is considerably closer to the full Cl than is CISDT. In fifth order the additional con-... [Pg.90]

SCF MBPT(2)- SDQ- MBPT(4)" CCSD - MBPT(4)" CCSD(T) Molecule Bond or angle... [Pg.111]

R. J. Bartlett and G. D. Purvis, III, Int. ]. Quantum Chem., 14, 561 (1978). Many-Body Perturbation Theory, Coupled Pair Many-Elearon Theory, and the Importance of Quadruple Excitations for the Correlation Problem. [SDQ-MBPT(4), CCD]. [Pg.163]

CC theory is inherently better than an equivalent level of Cl because it eliminates unlinked diagrams and as a consequence, is size-extensive [13]. It is also inherently better than an equivalent level of MBPT because it is not hmited to finite-orders, or potential difficulties encountered in the convergence of perturbation theory. It is well known, e.g. that ordinary MP perturbation theory does not converge for the electron gas, and this has also been emphasized recently for molecules [47], though resummations (including CC theory) work fine [48]. But, the operable word is equivalent level . For Cl, that meant at least single and double excitations, and frequently some more, perhaps even from a multi-reference space. MBPT had been done with single excitations in fourth-order SDQ-MBPT(4) in the above two papers [13,46]. [Pg.1197]

J. Gauss, Chem. Phys. Lett., 229, 198 (1994). G1A0-MBPT(3) and GIAO-SDQ-MBPT(4)... [Pg.254]

Correlation methods utilizing RHP and UHF reference determinants, including MBPT(2), MBPT(3), SDQ-MBPT(4), MBPT(4), CCD, CCSD, CCSD(T), CCSD+TQ (CCSD), CCSD(TQ), CCSDT-1 CCSDT-2, CCSDT-3, QCISD, QCISD(T), QCISD(TQ), UCCS(4), UCCSD(4), CID, and CISD. [Pg.622]

The (5s4p2d/3slp) Slater orbital (STO) basis has been used in a study of the quartic force field of H20. These calculations are done using SCF, SD-CI, and with various many-body models. The theoretical results agree well with the experimental force constants, with the many-body values showing better agreement than SD-CI. In fact, the most recent experimental and normal coordinate study revises several of the previously accepted force constants to be more consistent with these theoretical calculations. All of the cubic and quartic constants are determined from the calculations, while the experimental studies typically set many of these constants to zero to facilitate obtaining the force field from the normal coordinate analysis. Hence, the computed SDQ-MBPT(4) quartic force field for H2O is used as input to the local description of H2O in the 0 + H2O surface fit. This is described in detail in section IV. [Pg.775]


See other pages where SDQ-MBPT is mentioned: [Pg.115]    [Pg.107]    [Pg.109]    [Pg.100]    [Pg.88]    [Pg.91]    [Pg.95]    [Pg.96]    [Pg.96]    [Pg.97]    [Pg.107]    [Pg.118]    [Pg.119]    [Pg.119]    [Pg.119]    [Pg.566]    [Pg.244]    [Pg.2]    [Pg.137]    [Pg.138]    [Pg.139]    [Pg.141]    [Pg.142]    [Pg.143]    [Pg.149]    [Pg.151]    [Pg.152]    [Pg.154]    [Pg.161]    [Pg.774]    [Pg.775]    [Pg.775]    [Pg.776]    [Pg.776]    [Pg.776]    [Pg.776]    [Pg.776]   
See also in sourсe #XX -- [ Pg.4 , Pg.90 , Pg.95 , Pg.96 , Pg.107 , Pg.111 , Pg.116 , Pg.118 , Pg.119 ]




SEARCH



MBPT

© 2024 chempedia.info