The localized and the canonical variants of the many-body perturbation theory are used to calculate the energy corrections through fourth order for C14H14 in Pariser--Parr--Pople approximation, for a wide range of the coupling constant/]. The behaviour of the iocalization terms is examined. It is shown how the nonlocal cont¡ to the correlation energy can be gradually separated. The strictly local contribution left behind is surprisingly large: more than 50% of the total correlation energy. IntrodnctionAs is well known the wavefunctions determined by the Hartree---Fock (HF) method are not suitable to calculate acr values for the energy quantities of the valence shell (elr affinities, ionization and binding energies, etc.). In the last two decades various procedures have been developed which go beyond the independent particle seheme. One of the most straightforward approaches for taking into ar correlation effects is the diagrammatic many-body perturbation theory [1--3]. Ir can be used routinely for small molecules through third order in the energy (including some fourth order temas) [4 6]. Recently, with moderately sized basis sets the evaluation of ail fourth order temas has become feasible [7,8]. Except for some model systems, the calculation of all temas o f a given order lª than the fourth is out of question at present. There exist procedures, however, in which certain types of terms ate summed over to infinite order (CPMET [9,10], CEPA [11,12], and the method of Green's functions [13,14]).Previously it was conjectured that local and nonlocal r can be clr separated and that the former predominate [15]. One.of the authors of the present article (E.K.) developed a perturbation theory whose zeroeth order wavefunction is the APSG ground state [16]

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Various studies have been drawn toward the beneficial properties of fruit juices because they have several components, such as phenols, vitamins, and flavonoids, with antioxidant effects. However, fruit juices can also contain residues of pesticides used as standard pest control methods in crops. Many of these pesticides are degraded through oxidative mechanisms, and their persistence in juices can be enhanced by antioxidants. This study covers the degradation of four pesticides, aldicarb, demeton-S-methyl, fenamiphos, and methiocarb, to their respective sulfoxide and sulfone in grape juices, water (pH 3.5) and water (pH 3.5) with quercetin (one of the most important flavonoids of grape) added in an attempt to establish whether the presence of antioxidants can affect the degradation rate of pesticides. For this purpose, a multiresidue method based on solid-phase extraction (SPE) was developed for the simultaneous determination of these pesticides and their metabolites in commercial juices. The extraction procedure was carried out in C(18) columns. The subsequent elution of pesticides was performed with dichloromethane prior to the determination by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using two precursor-product ion transitions. Average recoveries for all the pesticides studied were higher than 80%, with relative standard deviations lower than 15% in the concentration range 0.005-0.05 microg/mL, and the quantification limits achieved ranged from 0.1 to 4.6 microg/L. The results demonstrated that degradation was slower in fruit juices and aqueous solutions with quercetin than in water. Several commercial grape juices were also analyzed to establish the levels of these pesticides. Methiocarb, fenamiphos, and demeton-S-methyl were found at low levels in some samples.