Use of the CNDO Method in Spectroscopy. I. Benzene, Pyridine, and the Diazines
15 Feb 1968-Journal of Chemical Physics (American Institute of Physics)-Vol. 48, Iss: 4, pp 1807-1813
TL;DR: In this article, the CNDO method was modified by substitution of semi-empirical Coulomb integrals similar to those used in the Pariser-Parr-Pople method, and by introducing a new empirical parameter κ to differentiate resonance integrals between σ orbitals from those between π orbitals.
Abstract: The CNDO method has been modified by substitution of semiempirical Coulomb integrals similar to those used in the Pariser‐Parr‐Pople method, and by the introduction of a new empirical parameter κ to differentiate resonance integrals between σ orbitals from those between π orbitals. The CNDO method with this change in parameterization is extended to the calculation of electronic spectra and applied to the isoelectronic compounds benzene, pyridine, pyridazine, pyrimidine, and pyrazine. The results obtained were refined by a limited CI calculation and compared with the best available experimental data. It was found that the agreement was quite satisfactory for both n→π* and π→π* singlet‐singlet transitions. The relative energies of the pi and lone‐pair orbitals in pyridine and the diazines are compared and an explanation proposed for the observed orders. Also, the nature of the “lone pairs” in these compounds is discussed.
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TL;DR: An LCAO-MO-SCF-CI model based on the lines introduced by Del Bene and Jaffe is developed in this article that is capable of reproducing the better identified observed spectra of nitrogen heterocycles with a rms error of ∼ 1000 cm−1.
Abstract: An LCAO-MO-SCF-CI model along the lines introduced by Del Bene and Jaffe is developed that is capable of reproducing the better identified observed spectra of nitrogen heterocycles with a rms error of ∼ 1000 cm−1. The model is applied to the spectra of pyrrole, benzene, pyridine, the diazines, symmetric triazine and symmetric tetrazine. The benzene and pyridine spectra are reproduced nearly exactly. The band observed in pyrrole at ∼ 6.5 eV is calculated as two bands at ∼ 6.5 eV, but they are assigned π→σ
* and not π→π. No evidence is found for the low lying 1
B
2g
in pyrazine, reported at ∼ 30400 cm−1 in pure crystals. The lowest excited singlet of sym. triazine is calculated as 1
E″ (n→π
*), not 1
A″2 (n→π), in agreement with a recent interpretation of Fischer and Small. Several bands are reassigned, and the electronic nature of the transitions discussed. Naphthalene and quinoxaline are examined to insure that no large drift of results are met with molecules of other sizes. Comparison of eigenvalues with molecular ionization potentials is made. Here the numerical agreement appears satisfactory for the first few ionization potentials only.
1,739 citations
TL;DR: A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described in this paper, which is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3D atomic orbitals.
Abstract: A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described. The model is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3d atomic orbitals. The model is within the unrestricted Hartree-Fock formalism, and a method for spin purification is described. Problems with convergence of the self-consistent field are discussed, and a method that has been found successful in aiding the convergence is outlined. The model has been applied to many transition metal systems. In this article the results of calculations on the chlorides of Fe, Co and Cu are described. The results of these calculations are compared with experiment, and with the results of calculations by other methods.
681 citations
TL;DR: In this paper, the intermediate neglect of differential overlap technique is modified and applied to the calculation of excited triplet states, and the resulting method generally reproduces the transition energies of the better-classified observations within a rms error of 1000 cm−1.
Abstract: The intermediate neglect of differential overlap technique is modified and applied to the calculation of excited triplet states. The resulting method generally reproduces the transition energies of the better-classified observations within a rms error of 1000 cm−1. Trends are well reproduced, and the calculated orders ofn-π* and π-π* triplet states are in good accord with the experimental information to date. The method is applied to benzene and the azines. The lowest four triplet states of benzene are calculated in good accord with experiment. Pyridine is calculated to have an-π* triplet nearly degenerate with the lowest lying π-π* triplet, corroborating suggestions of Japar and Ramsay based on experimental information. A detailed analysis is made of the diazines, and assignments are suggested for the higher lying triplet states not yet classified or not yet observed.
560 citations
TL;DR: In this paper, a review of the basic concepts and calculation methods of the "anionic group theory for the nonlinear optical effect of crystals" and a brief discussion of the approximations involved are presented.
Abstract: Starting from a general quantum-mechanical perturbation theory on the nonlinear optical (NLO) effect in crystals, this review gives a systematic presentation of the basic concepts and calculation methods of the ‘anionic group theory for the NLO effect of crystals’ and a brief discussion of the approximations involved. Calculations have been made for the second harmonic generation (SHG) coefficients of a few typical NLO crystals. Comparisions between these theoretical values and the experimental values made both on powdered crystals and on single crystals suffice to show the feasibility of the theoretical treatment and calculation methods. On this basis, borate ions of various structure types are classified and systematic calculations are carried out for the NLO susceptibilities of some typical borate crystals with good prospects of applications in opto-electronics. Through these calculations, a series of structural criteria serving as useful guidelines for searching and developing new NLO crystal...
430 citations
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4,691 citations
TL;DR: In this paper, the authors modified the self-consistent molecular orbital theory with complete neglect of differential overlap (CNDO) presented in earlier papers and applied it to symmetrical triatomic (AB2) and tetratomic (AB3) molecules.
Abstract: The approximate self‐consistent molecular orbital theory with complete neglect of differential overlap (CNDO) presented in earlier papers has been modified in two ways. (a) Atomic matrix elements are chosen empirically using data on both atomic ionization potentials and electron affinities. (b) Certain penetration‐type terms, which led to excess bonding between formally nonbonded atoms in the previous treatment, have been omitted. The new method (denoted by CNDO/2) has been applied to symmetrical triatomic (AB2) and tetratomic (AB3) molecules, for a range of bond angles. The theory leads to calculated equilibrium angles, dipole moments, and bending force constants which are in reasonable agreement with experimental values in most cases.
1,782 citations
1,718 citations
TL;DR: In this article, the theory of electronic spectra and electronic structure was further developed and applied to ethylene, butadiene, benzene, pyridine, pyrimidine, pyrazine, and s-triazine.
Abstract: The theory of electronic spectra and electronic structure, the elucidation of which was begun in the first paper of this series, is further developed and applied to ethylene, butadiene, benzene, pyridine, pyrimidine, pyrazine, and s‐triazine.A realistic and consistent LCAO‐MO π‐electron theory should allow the σ‐electrons to adjust themselves to the instantaneous positions of the mobile π‐electrons. This is accomplished in the theory by assignment of empirical values to the Coulomb electronic repulsion integrals and Coulomb penetration integrals which enter the formulas, these values being obtained in a prescribed way from valence state ionization potentials and electron affinities of atoms. Use of the empirical values in the molecular orbital theory reduces the magnitude of computed singlet‐triplet splittings and the effects of configuration interaction without complicating the mathematics. From the valence‐bond point of view, ionic structures may be said to be enhanced.The applications to hydrocarbons a...
1,514 citations