Semi-empirical Parameters in pi-Electron Systems. I. Method and Application to Pure Hydrocarbons.

Roos, Bjoern O.; Skancke, P. N.; Alnås, Åke; Hemmingsson, Sten; Kullberg, Lennart; Blinc, R.; Paušak, S.; Ehrenberg, L.; Dumanović, J.

doi:10.3891/acta.chem.scand.21-0233

Cited by 61 publications

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“…A@roximntion Ib: The result of removing degeneracy, by mixing of all singly excited configurations shows (Figure 3b) that the order in which the electronic levels appear is, in this case, the same as that found (Figures 2c, e and f ) in the earlier papers of references [6], [16] and [17] (with the exception of the excited lA, level not well specified in those papers).…”

Section: Resultssupporting

confidence: 72%

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Theoretical study of the derivative hydrocarbons of biphenylene. I. Electronic spectrum of the biphenylene

Peradejordi¹,

Domingo

Ferńndez‐Alonso

1969

Int J of Quantum Chemistry

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AbstractsThe electronic spectrum of biphenylene has been studied theoretically. The investigation is based on the semi-empirical LCAO SCF MO method with various degrees of approximations. The results have been analysed with regard to the following two factors: ( a ) The difference in effective electronegativity between the carbon atoms in the four-membered ring and the other carbon atoms in the molecule. ( b ) The inclusion of doubly excited configurations in the description of the n-electronic molecular states. The theory satisfactorily interprets the excitation energies and the nature of the electronic transitions. The predictions are particularly affected by the inclusion of the doubly excited configurations. On the basis of these results, the empirical parameters used are discussed.Une ttude thkorique du spectre tlectronique du biphenylhe est donnee. Cette ttude est baste sur la mtthode semi-empirique LCAO SCF MO avec difftrents niveaux d'approximation. L'effet des deux facteurs suivants sur les rtsultats est analyst: ( a ) La difference d'electrontgativitt effective entre les atomes de carbone dans le cycle tetra-atomique et les autres carbones de la moltcule. ( b ) L'inclusion de configurations doublement excittes dans la description des ttats n-tlectroniques. La thtorie interprete de fason satisfaisante les energies d'excitation et la nature des transitions Clectroniques. L'inclusion des configurations doublement excitkes s'avere un des facteurs essentiels A I'interprttation des donntes expCrimentales. Sur la base de ces rtsultats, on discute les parametres empiriques utilists.

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Section: Resultssupporting

confidence: 72%

“…where W, is the ionization potential for the n-orbital in the planar CH, radical [16,281. By substituting one of the hydrogen atoms by an sp2 sr-hybridized carbon atom C, at the benzene C-C distance, R, we have for the new ionization potential the value:…”

Section: Methods and Technique Of Calculationmentioning

confidence: 99%

Theoretical study of the derivative hydrocarbons of biphenylene. I. Electronic spectrum of the biphenylene

Peradejordi¹,

Domingo

Ferńndez‐Alonso

1969

Int J of Quantum Chemistry

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“…All details concerning the carbon parameters have been published elsewhere by two of us (B. R. and P. N. S.) [4]. Here, we shall only review the results briefly and report on some recent, minor modifications.…”

Section: B Carbon Parametersmentioning

confidence: 99%

Semiempirical studies of metal complexes of biological importance

Fischer‐Hjalmars¹,

Grabe²,

Roos³

et al. 2009

Int. J. Quantum Chem.

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The biological activity of some metal complexes, especially the metal porphyrins, is discussed.Since previous theoretical investigations of these compounds are rather incomplete in several respects, a modified semiempirical method of treating metal complexes has been developed. In particular, this modification includes the dependence of the parameter W,, upon the surroundings. Parameter values appropriate to carbon and nitrogen are given. Some results, obtained in application to comparatively simple compounds, especially copper dimethylglyoxime, are reported.

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“…Roos & Skancke (1967) have predicted that secondorder shifts should occur in structures of this type. An INDO calculation yielded gross Mulliken populations which are included in Fig.…”

Section: P-terphenylmentioning

confidence: 99%

Charge-density analyses for molecular crystals using Bragg diffraction data: the effects of error

Allen‐Williams¹,

Delaney²,

Furina³

et al. 1975

Acta Cryst Sect A

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Charge-density analyses have been carried out on twelve sets of X-ray data. For materials containing first-row atoms intensities measured by the 0:20 method yield gross populations concordant with electronegativities and the shapes of the distributions agree qualitatively with predicitions from forcefield arguments. Gross charges are sensitive to experimental errors systematic with Bragg angle, but are insensitive to deficiencies in the models for thermal motion. Noise in thermal parameters is a limiting factor for hydrogen populations determined from X-ray data alone, but mechanistic models for the hydrogen motions obviate this difficulty. Spherically symmetric functions centred at the nuclei give a poor representation of the density for bonded hydrogen. Slater-type orbital products with standard molecular exponents sample the valence density less efficiently for second-row atoms than for carbon, nitrogen and oxygen atoms. Two-centre density functions overlap heavily with neighbouring one-centre terms, and do not provide a useful extension to basis sets for charge-density studies. There are discrepancies between experimental populations and semi-empirical INDO calculations for strongly polar systems.

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Semi-empirical Parameters in pi-Electron Systems. I. Method and Application to Pure Hydrocarbons.

Cited by 61 publications

References 0 publications

Theoretical study of the derivative hydrocarbons of biphenylene. I. Electronic spectrum of the biphenylene

Theoretical study of the derivative hydrocarbons of biphenylene. I. Electronic spectrum of the biphenylene

Semiempirical studies of metal complexes of biological importance

Charge-density analyses for molecular crystals using Bragg diffraction data: the effects of error

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