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Volumn 112, Issue 18, 2000, Pages 7873-7879

Some surprising failures of Brueckner coupled cluster theory

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EID: 0001608093     PISSN: 00219606     EISSN: None     Source Type: Journal    
DOI: 10.1063/1.481424     Document Type: Article
Times cited : (59)

References (77)
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  • 44
    • 85037511497 scopus 로고    scopus 로고
    • note
    • The EOMIP - CCSD method is equivalent to the Fock-space multireference coupled cluster method based on single and double excitations (FSMRCCSD) when the latter is applied to singly ionized states.
  • 55
    • 0004040381 scopus 로고
    • The package also contains modified versions of the MOLECULE Gaussian integral program of J. Almlöf and P. R. Taylor, the ABACUS integral derivative program written by T. U. Helgaker, H. J. Aa. Jensen, P. Jørgensen, and P. R. Taylor, and the PROPS property evaluation integral code of P. R. Taylor
    • J. F. Stanton, J. Gauss, J. D. Watts, W. J. Lauderdale, and R. J. Bartlett, ACES II, 1993. The package also contains modified versions of the MOLECULE Gaussian integral program of J. Almlöf and P. R. Taylor, the ABACUS integral derivative program written by T. U. Helgaker, H. J. Aa. Jensen, P. Jørgensen, and P. R. Taylor, and the PROPS property evaluation integral code of P. R. Taylor.
    • (1993) ACES II
    • Stanton, J.F.1    Gauss, J.2    Watts, J.D.3    Lauderdale, W.J.4    Bartlett, R.J.5
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    • note
    • -1.
  • 72
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    • When the state of interest lies just above that which interacts with it, negative force constants can be found at the CC level. This is in contrast to the first-order pole structure which must be followed in an exact theory. Analysis of the CC second derivative expression shows that this unphysical term vanishes in the limit that the two states are related by a pure single excitation and is expected to be small when there is not a significant contribution from double excitations (Ref. 75). A very limited set of exploratory calculations suggests that the effects of this term are found only near the singularity in such cases, when the gap between the two states is smaller than the vibronic coupling strength. A more detailed exposition of these effects will be published in the future
    • There is also a term that is formally quadratic in the derivative T̂ amplitudes which contributes to the second derivative of the CC energy. This term is responsible for the unphysical behavior that is seen beyond the singularity in the plot of force constant vs coordinate in Fig. 1. It should be noted that this term has also been discussed within the context of the so-called quadratic EOM - CC approach to second-order properties [S. A. Perera, M. Nooijen, and R. J. Bartlett, J. Chem. Phys. 104, 3290 (1996)]. When the state of interest lies just above that which interacts with it, negative force constants can be found at the CC level. This is in contrast to the first-order pole structure which must be followed in an exact theory. Analysis of the CC second derivative expression shows that this unphysical term vanishes in the limit that the two states are related by a pure single excitation and is expected to be small when there is not a significant contribution from double excitations (Ref. 75). A very limited set of exploratory calculations suggests that the effects of this term are found only near the singularity in such cases, when the gap between the two states is smaller than the vibronic coupling strength. A more detailed exposition of these effects will be published in the future.
    • (1996) J. Chem. Phys. , vol.104 , pp. 3290
    • Perera, S.A.1    Nooijen, M.2    Bartlett, R.J.3
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    • note
    • 2 radicals.
  • 76
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    • note
    • Of course, this is not the only difference between B - CC and standard CC methods, as the numerators (which represent approximations to vibronic coupling strengths) are also different from those involving coupling of the reference and EOM states in the latter. In addition, there is clearly a second-order contribution between force constants and B - CC ER matrix eigenvalues that can be seen in Fig. 1. Although the mathematical structure of the B - CC second derivative equations is extremely complicated and has not been analyzed in detail, limited empirical evidence suggests that the second-order contribution to B - CC force constants is somewhat larger than that for standard CC methods.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.