Rafael B. de Almeida

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In this work, we have explored the validity of the hypotheses on which rest the Hammett's approach to quantify the substituent effect on a reaction center, by applying two DFT energy decomposition schemes. This is performed by studying the change in the total electronic energy, ΔΔE, associated with a proton transfer isodesmic equilibrium. For this reaction,(More)
In this paper we study the manifestations of cooperative effects in the formation of clusters4-methyloxycarbonyl2-azetidinone. Structural properties of the clusters were obtained at the DFT/B3LYP/6-311G(d) level of calculation, while the energetic ones were calculated at the B3LYP/6-311G(d), B3LYP/6-31++G(d,p) and HCTH407/6-31++G(d,p) DFT levels. The(More)
The study of magnetic phenomena in nanometer scale is essential for development of new technologies and materials. It also leads to a better understanding of magnetic properties of matter. An approach to the study of magnetic phenomena is the use of a physical model and its computational simulation. For this purpose, in previous works we have developed a(More)
In this work, using a valence-bond wave function we obtain analytical expressions for the first- and second-order reduced density matrices of two simple, but quite representative, cases of diatomic molecular systems, namely, H2 and LiH. A detailed study of their exchange-correlation density is performed for both equilibrium and nonequilibrium internuclear(More)
In this work we have explored the performance of two functions, recently proposed by Ayers [J. Chem. Sci., 2005, 117, 441], with the purpose of quantifying local electron localization. The first function, ζ(h), measures the total fluctuation per electron in the number of electrons at a given position r(1), while the second one, ζ(R), is a local(More)
The sigma delocalization plays an important role in the stability of small boron clusters; therefore, it is important to establish under which circumstances this delocalization contributes to the aromaticity of these molecules. In this work, using electron localization function (ELF) calculations, we show that sigma and pi electrons follow different(More)
In this work, we propose the application of a self-consistent extended Huckel tight-binding (EHTB) method in the computation of the absorption optical spectrum of molecules within the linear response time dependent density functional formalism. The EHTB approach is presented as an approximation to the Kohn-Sham energy functional. The method is applied to(More)
Recently, multi component crystals composed of two or more molecules that form a unique crystalline structure having unique phase and properties, where its components are bond together via hydrogen bonds, have been the subject of great deal of attention, in particular those where aminoacids participate in their structure. In this work we have studied a(More)