Comparing ab initio density-functional and wave function theories: the impact of correlation on the electronic density and the role of the correlation potential

The framework of ab initio density-functional theory (DFT) has been introduced as a way to provide a seamless connection between the Kohn-Sham (KS) formulation of DFT and wave-function based ab initio approaches [R. J. Bartlett, I. Grabowski, S. Hirata, and S. Ivanov, J. Chem. Phys. 122, 034104 (2005)]. Recently, an analysis of the impact of dynamical correlation effects on the density of the neon atom was presented [K. Jankowski, K. Nowakowski, I. Grabowski, and J. Wasilewski, J. Chem. Phys. 130, 164102 (2009)], contrasting the behaviour for a variety of standard density functionals with that of ab initio approaches based on second-order M?ller-Plesset (MP2) and coupled cluster theories at the singles-doubles (CCSD) and singles-doubles perturbative triples [CCSD(T)] levels. In the present work, we consider ab initio density functionals based on second-order many-body perturbation theory and coupled cluster perturbation theory in a similar manner, for a range of small atomic and molecular systems. For comparison, we also consider results obtained from MP2, CCSD, and CCSD(T) calculations. In addition to this density based analysis, we determine the KS correlation potentials corresponding to these densities and compare them with those obtained for a range of ab initio density functionals via the optimized effective potential method. The correlation energies, densities, and potentials calculated using ab initio DFT display a similar systematic behaviour to those derived from electronic densities calculated using ab initio wave function theories. In contrast, typical explicit density functionals for the correlation energy, such as VWN5 and LYP, do not show behaviour consistent with this picture of dynamical correlation, although they may provide some degree of correction for already erroneous explicitly density-dependent exchange-only functionals. The results presented here using orbital dependent ab initio density functionals show that they provide a treatment of exchange and correlation contributions within the KS framework that is more consistent with traditional ab initio wave function based methods.     

MBPT and coupled cluster calculation on the neon atom with numerical orbitals

Our diatomic coupled cluster method with numerical orbitals has been applied to the Ne atom. Second, third, and full fourth order MBPT correlation corrections as well as coupled cluster correlation energies are reported.     

An investigation of the effects of pressure and temperature on the vapourization characteristics of crude oil using first approximation thermal analysis

This study investigates the effect of pressure and temperature on crude oil vaporization using first approximation thermal analysis. Developed here is a technique for quantifying the vaporization of fractions of a crude oil using an experimentally obtained thermogravimetric (TG) curve of the crude.The initial data utilized is the weight loss versus temperature values at atmospheric pressure, together with physical property data and equilibrium constant,k values.The results of this study allow the estimation of the volume of oil distilled underground when steam is injected into oil reservoirs at varying pressures and temperatures to recover crude oil.

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Zusammenfassung Diese Studie untersucht in erster Näherung mittels Thermoanalyse den Einfluß von Temperatur und Druck auf das Verdampfen von Rohöl. Es wird eine Methode zur quantitativen Bestimmung des Verdampfens von Rohölfraktionen entwickelt, die auf einer experimentell ermittelten thermogravimetrischen (TG) Kurve des Rohstoffes basiert. Als Anfangswerte werden die von der Temperatur abhängige Massenabnahme (unter Normaldruck) zusmmmen mit physikalischen Eigenschaften und der Gleichgewichtskonstantek verwendet. Die Ergebnisse dieser Untersuchung erlauben das Abschätzen des Umfanges des Öldestillationsrückstandes, insofern zur Gewinnung des Rohols Dampf in die Ölreservoir injeziert wird.

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Chiroptische Eigenschaften und Äquilibrierungen stereoisomerer Yohimbane und ihrer 17-Ketoderivate

The chiroptical properties (CD. and ORD.) of four stereoisomeric yohimbanes ( 1–4 ) and the corresponding 17-keto derivatives 5–8 have been studied. The aromatic and the ketonic Cotton effects have been considered in terms of the appropriate Sector and Octant Rules, respectively. Positively charged nitrogen makes an ‘anti-octant’ contribution to the ketonic Cotton effect. The chiroptical properties, the NMR. spectra and dehydrogenation reactions with mercuric acetate together indicate the presence of a C/D-trans-quinolizidine system in all the compounds studied, except those of the pseudo series ( 3 and 7 ), in which a C/D-cis-quinolizidine system is present. An explanation of the unexpectedly slow dehydrogenation of the 3-epi-allo compounds 4 and 8 is suggested. Conformational analysis of the results of equilibration experiments on pairs of 3-epimeric compounds (in both glacial acetic acid at 145° and in K-t-butylate at 211°) leads independently to conclusions which agree with those drawn from the physical methods. The great differences between the equilibrium positions of the free bases and the protonated forms are due to the presence in the latter cases of oriented ion pairs R₃N⁺H…?^?O₂CCH₃.     

The growth of ice crystals in an electric field

Zusammenfassung Das Wachstum von Eiskristallen in einer Diffusionswolkenkammer wird durch ein elektrisches Feld von über 500 V/cm wesentlich geändert. Die Kristalle wachsen sehr schnell in Form langer, dünner Nadeln. Die Ursache des beschleunigten Wachstums ist noch nicht völlig erkannt; aber die Beobachtungen stimmen mit der Hypothese überein, dass die Kristalle durch Einbau von neutralen Wassermolekülen wachsen.     

RPA and the linear hubbard model

The accuracy of RPA is tested semi-empirically by comparison with full Cl.     

Search for ZH → l+ l- bb production in 4.2 fb(-1) of pp collisions at sqrt[s] =1 .96 TeV

We present a search for the standard model Higgs boson produced in association with a Z boson in 4.2 fb(-1) of pp collisions, collected with the D0 detector at the Fermilab Tevatron at sqrt[s] =1 .96 TeV. Selected events contain one reconstructed Z → e+ e- or Z → μ+ μ- candidate and at least two jets, including at least one b-tagged jet. In the absence of an excess over the background expected from other standard model processes, limits on the ZH cross section multiplied by the branching ratios are set. The limit at M(H) = 115 GeV is a factor of 5.9 larger than the standard model prediction.