Pariser-Parr-Pople calculations

Pariser-Parr-Pople calculations, 72 calculations of thiazolocyanines, 73 of thiazolium salts, 31 Pentamethine thiazolocyanines, chain-bridged, synthesis of. 58 cleavage of, 63 nomenclature of. 26 synthesis of, 56... 

Many such expressions have been suggested, most of them in the context of the Pariser-Parr-Pople calculations for n conjugated species. We describe below most of the approximations which were found suitable even though some of them have not been used in the methods designed for a bonded molecules. 

This method has been extensively used in Pariser-Parr-Pople calculations on conjugated systems. It has also been employed by Jaffe 31> in his parameterization of CNDO/2. 

Ohno 40> has suggested the following empirical relationship which he applied to Pariser-Parr-Pople calculations... 

Pariser-Parr-Pople calculations on different UNA constituents. Theoret. Chim. 

Their calculated value for the 7r-ionization potential was 14.111 eV no experimental value is available. Galasso94 has also used Pariser-Parr Pople calculations on the three benzoquinolizinium ions to produce charge densities and transition energies. Molecular orbital calculations of LUMO and HOMO levels in the benzo[/>]quinolizinium ion have been used in a discussion of the mechanism of cationic polar cycloaddition (Section IV,E).95 The binding energy of the positive nitrogen in the benzoquinolizinium salts has been measured relative to that of nitrate, and has been found to be 7.8-8.1 eV.96... 

Figure 7.1 Plot of the semi-empirical Ea versus the experimental Ea for the linear acenes 1 to 9. The squares are the CURES-EC values that are equal to the experimental values within the uncertainties [8], The x s stand for the Pariser Parr Pople calculated values [10]. The latter have systematic uncertainties that vary with magnitude.

Table 11.2 The experimentally determined and theoretical predictions of the low-lying vertical excitations of benzene (in eV) (The experimental assignments are from (Bursill et al. 1998). Pariser-Parr-Pople calculations with t = 2.539 eV, and U = 10.06 eV (Bursill et al. 1998).)...

Figure 15 Topologically chiral interlocked molecules that were studied by CD. (a) The structures of the ahnost-symmetrical supermolecules that exhibited pronounced CD signals, (b) The absolute configuration of knot-type molecule 28 was determined by TDPPP (time-dependent Pariser-Parr-Pople) calculation of the CD spectrum of a fully optimized AMI geometry.

OPW (orthogonalized plane wave) a band-structure computation method P89 (Perdew 1986) a gradient corrected DFT method parallel computer a computer with more than one CPU Pariser-Parr-Pople (PPP) a simple semiempirical method PCM (polarized continuum method) method for including solvation effects in ah initio calculations... 

Indazoles have been subjected to certain theoretical calculations. Kamiya (70BCJ3344) has used the semiempirical Pariser-Parr-Pople method with configuration interaction for calculation of the electronic spectrum, ionization energy, tt-electron distribution and total 7T-energy of indazole (36) and isoindazole (37). The tt-densities and bond orders are collected in Figure 5 the molecular diagrams for the lowest (77,77 ) singlet and (77,77 ) triplet states have also been calculated they show that the isomerization (36) -> (37) is easier in the excited state. 

Simple HMO calculations (68JCS(B)725) satisfactorily account for the UV spectra of a great number of pyrazoles substituted by methyl and phenyl groups. The spectra of pyrazolium and indazolium salts (free bases in IN HCl) have been compared with calculated transitions (Pariser-Parr-Pople method) (74MI40403). 

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 to differentiate resonance integrals between a orbitals and tt 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, pyri-dazine, pyrimidine and pyrazine. The results obtained were refined by a limited Cl calculation, and compared with the best available experimental data. It was found that the agreement was quite satisfactory for both the n TT and n tt singlet transitions. The relative energies of the tt and the 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. 

A method which is similar to the Pariser-Parr-Pople method for the n electron system and is applicable to common, saturated molecules has been proposed by Pople 28>. This method is called the CNDO complete neglect of differential overlap) SCF calculation. Katagiri and Sandorfy 29> and Imamura et al. °) have used hybridized orbitals as basis of the Pariser-Parr-Pople type semiempirical SCF calculation. 

Qualitatively, similar relationships are ascertained in heteroaromatic systems where the same conclusion is derived by a numerical calculation. In more elaborate calculations than the Hiickel method, such as the Pariser-Parr-Pople approximation 21>23>, similar distinct parallelisms are recognized 59> (Table 4.1). Essentially the same circumstances exist also... 

One example showing a serious discrepancy of the frontier electron method was reported by Dewar H8,ii9). This is 10,9-borazaphenanthrene, and the value of / -B) was reported to have been calculated by the Pople method, but the parameters usyd were not indicated. Fujimoto s calculation by the Pariser-Parr-Pople method 120>, in perfect disagreement with Dewar s, gives the most reactive position as 8, which parallels experiment. The ambiguity involved in the integral values adopted seems to be serious, so that the establishment of parametrization for boron heterocycles is desirable. 

When parameters of the Pariser-Parr-Pople configuration interaction molecular orbital (PPP-CI MO) method were modified so as to reproduce the Aol)s values for l,3-di(5-aryl-l,3,4-oxadiazol-2-yl)benzenes 16 and 17, the calculated HOMO and LUMO energy levels corresponded with the experimental ionization potential and electron affinity values. The relationships between the electrical properties and molecular structures for the dyes were investigated. The absorption maximum wavelengths for amorphous films were found to be nearly equal to those for solution samples <1997PCA2350>. 

The dipole moment calculated for 111 is somewhat higher than for 96, as expected. The total it charge in the cyclopentadiene ring is calculated to be 0.54 electrons. A somewhat smaller polarization, 0.40 tt electrons, is calculated for 7,8-diphenylcalicene (124), and 0.34 tt electrons for hexaphenylcalicene 115, (122) by the PPP (Pariser-Parr-Pople) method. Thus it seems as if the tt polarization roughly follows the same trend as the bond lengths and the C=C torsional barriers. 

The calculations were carried out by J. J. C. Mulder, Leiden, according to the Pariser-Parr Pople method and were rounded off by taking into account configuration-interaction of all singly excited states. See Ref. i 2) fQj- results. 

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