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Volumn 118, Issue 15, 2003, Pages 6874-6883

Electronic structure of the trimethylenemethane diradical in its ground and electronically excited states: Bonding, equilibrium geometries, and vibrational frequencies

Author keywords

[No Author keywords available]

Indexed keywords

APPROXIMATION THEORY; CALCULATIONS; CHEMICAL BONDS; COMPUTATIONAL METHODS; ELECTRONIC DENSITY OF STATES; ELECTRONIC STRUCTURE; ELECTRONS; ETHYLENE; FREE RADICALS; GROUND STATE; MOLECULAR VIBRATIONS; WAVE EQUATIONS;

EID: 0037623374     PISSN: 00219606     EISSN: None     Source Type: Journal    
DOI: 10.1063/1.1561052     Document Type: Article
Times cited : (91)

References (108)
  • 9
    • 0003691440 scopus 로고
    • edited by W. T. Borden (Wiley, New York)
    • Diradicals, edited by W. T. Borden (Wiley, New York, 1982).
    • (1982) Diradicals
  • 54
    • 0038683922 scopus 로고    scopus 로고
    • note
    • Note that due to the Pauli principle the spatial parts of singlets are symmetric with respect to the interchange of two electrons, whereas the spatial parts of triplets are antisymmetric. This causes all the two-electron triplet states to be purely covalent. The physical explanation of this formal result is that the Pauli principle does not allow two electrons with the same spin to coexist in the same volume of space, as required in ionic (or switter-ionic) configurations. The character of the single states depend on the nature of the orbitals, and can vary from purely ionic of purely covalent wave functions. A detailed analysis of the diradical wave functions can be found in Refs. 9, 49, 51-53.
  • 58
    • 0038007326 scopus 로고    scopus 로고
    • note
    • 3h TMM), unless state-averaged orbital optimization is performed.
  • 63
    • 0003748990 scopus 로고    scopus 로고
    • edited by K. Hirao (World Scientific, Singapore)
    • Recent Advances in Multireference Methods, edited by K. Hirao (World Scientific, Singapore, 1999).
    • (1999) Recent Advances in Multireference Methods
  • 80
    • 0038345419 scopus 로고    scopus 로고
    • note
    • We used the functional composed of the equal mixture of the following exchange and correlation parts: 50% Hartree-Fock+ 8% Slater+ 42% Becke for exchange, 19% VWN+ 81% LYP for correlation.
  • 86
    • 0004040379 scopus 로고
    • note
    • 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
  • 88
    • 0037669544 scopus 로고    scopus 로고
    • note
    • 2 states calculated from the triplet and quintet references are 6.005 and 4.610 eV, respectively.
  • 92
    • 0001181172 scopus 로고    scopus 로고
    • note
    • 2-hybridized atoms are available for bonding, the bond order increases due to π bonding, and the bond contracts further.
  • 95
    • 0038683889 scopus 로고    scopus 로고
    • note
    • The equilibrium structure of ethylene is calculated at the CCSD(T)/cc-pVTZ level. The experimental CC bond in the ethylene equals 1.339 Å (Ref. 107). The discrepancy is much larger than the method's intrinsic error of about 0.002 Å and is due to anharmonicity.
  • 96
    • 0038345375 scopus 로고    scopus 로고
    • note
    • 2 hybridized carbons
  • 99
    • 0038007334 scopus 로고    scopus 로고
    • note
    • Again, as in case of ethylene, the experimental (1.399 Å, Ref. 107) and high level theoretical (1.391 Å, Ref. 103) CC bond lengths are very different due to anharmonicities.
  • 104
    • 0037669546 scopus 로고    scopus 로고
    • note
    • The experimentally measured frequencies are the fundamentals, i.e., the energy differences between the zero and first vibrational levels. The calculated harmonic frequencies are equal to the fundamentals only for pure harmonic potentials. For a real anharmonic potential, the fundamental can be lower (this is often a case for stretching vibrations) or higher (as can happen for OPLA modes) than the harmonic frequencies. Morever, anharmonic terms can couple harmonic vibrational modes, which can strongly affect the observed intensities, e.g., some frequencies may not be observed due to anharmonicities.
  • 105
    • 0038683888 scopus 로고    scopus 로고
    • note
    • i.CCSD(T) × 100%.
  • 106
    • 0038345379 scopus 로고    scopus 로고
    • note
    • The SF-DFT IR intensities are not available because the analytic gradients for this method have not yet been implemented.
  • 107
    • 0038345380 scopus 로고    scopus 로고
    • note
    • -1.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.