Selecting a method to compute partial atomic charges is not trivial because different methods usually provide different charge values and there is no consensus on the most useful approach. In this work, Mulliken, MBS, Chelp, Chelpg, MK, Hirshfeld, NPA, DMA and AIM methods were selected to compute atomic charges and electric dipole moment vector of N-{N-(Pterin-7-yl)carbonylglycyl}-L-tyrosine molecule, a ricin inhibitor which has different types of bonds and chemical environments. While MBS and DMA methods provided the most chemically consistent charges according to atomic electronegativity and electron resonance effects criteria, Chelp, Chelpg and MK had the worst performances. Atomic charges and dipole moment calculated by the Hirshfeld method had the smallest magnitudes, a well-known behavior. Despite the differences among atomic charges predicted by all methods, the direction of the dipole moment vector was essentially the same. Further charge calculations using different basis sets and quantum methods indicated that the dependency on this aspect was the highest for Mulliken and Chelp and the lowest for MBS, Hirshfeld and DMA methods. Thus, results point to MBS and DMA as the most suitable methods for computing chemically consistent atomic charges and dipole moment vectors of similar systems for different applications; e.g., molecular dynamics.

We investigated theoretically the ground state electronic structure and the onset of molecular fragmentation of 1,1-diamino-2,2-dinitroethylene (FOX-7) using density functional theory. The molecular charge density was analyzed via two partition methods: the distributed multipole analysis (DMA) and the deformed atoms in molecules (DAM). In this framework, the push-pull effect, hydrogen intra-molecular bonding and site acid-base properties of the molecule were discussed. Our analysis indicates that the molecular origin of the low measured impact sensitivity of FOX-7 is due to the magnitude of multipole values of the C-N bonds in the NO2 groups, the delocalized electrons over the central C-C bond and the hydrogen bonds. The onset of FOX-7 decomposition and acid-base properties were examined with the nuclear Fukui functions. The results support nitro to nitrite rearrangement and direct release of a NO2 as a possible initial step in FOX-7 decomposition process. The approach suggested is general and can be especially useful for very large molecules to examine in detail their electronic structure and to guide the search for the decomposition mechanisms.

Um método teórico geral em duas etapas para estudar redistribuições eletrônicas em processos catalíticos é apresentado. Na primeira etapa, teoria do funcional da densidade (DFT) é usada para otimizar completamente duas geometrias: o aglomerado que representa o catalisador e o sistema aglomerado mais molécula adsorvida. Na segunda etapa, a densidade eletrônica molecular convergida é dividida em multipolos centrados em sítios atômicos obtidos segundo uma análise de multipolos distribuídos, que fornece informação topológica detalhada da redistribuição de carga do catalisador e da molécula, antes e depois da adsorção. Esta abordagem é aplicada para a adsorção de tiofeno sobre a borda metálica 10-10 dos catalisadores Ni(Co)MoS e comparada com a mesma reação em MoS2 não-substituído. Energias de adsorção, geometrias e a análise de multipolos calculada indicam uma fraca adsorção do tiofeno em ambas as situações. Um modelo coulombiano para a ligação química mostra que a magnitude da ligação metal-enxofre na superfície dos catalisadores de Ni(Co)MoS promovidos é consideravelmente menor do que em MoS2 não substituído, desta forma confirmando a origem do aumento da atividade de hidrodessulfurização (HDS) nestes catalisadores.

A general two-step theoretical approach to study electronic redistributions in catalytic processes is presented. In the first step, density functional theory (DFT) is used to fully optimize two geometries: the cluster representing the catalyst and the cluster plus adsorbed molecule system. In the second step, the converged electron density is divided into multipoles centered on atomic sites according to a distributed multipole analysis which provides detailed topological information on the charge redistribution of catalyst and molecule before and after adsorption. This approach is applied to thiophene adsorption on the 10-10 metal edge of Ni(Co)MoS catalysts and compared to the same reaction on bare MoS2. Calculated adsorption energies, geometries and multipole analysis indicate weak thiophene chemisorption on both cases. A Coulombic bond model showed that surface metal-sulfur bond strengths in Ni(Co)MoS promoted catalysts are considerably smaller than in bare MoS2, thus confirming the origin of the enhancement of hydrodesulfurization (HDS) activity in these catalysts.

Chemical agents are substances used for their toxic effects on humans, animals and plants. The main objective of chemical defense is to develop systems that reduce these effects while minimizing impact on the operational capacity of military troops. In this work, a report on the development of chemical warfare agents since the First World War and their classification is presented. Special attention is given to neurotoxic agents, the most lethal group of chemical agents known to date.

This article reviews previously employed methods to study several valence electronic transitions, optically forbidden or not, enhancing intensity through vibronic coupling. Electronic transition dipole moments were calculated using several ab initio methods including electron correlation. In this method the square of the electronic transition dipole moments are directly calculated along the normal coordinates of vibration and then expanded with a polynomial function. Afterwards, analytical vibrational integration using harmonic wave functions, of the square of the transition moments function, allows us to obtain partial (i.e. for each vibrational mode) and total optical oscillator strengths (OOS), for the vibronic transition of interest. We illustrate the accuracy of the method through valence transitions of benzene (C6H6), formaldehyde (H2CO), acetone (C3H6O) and formic acid (HCOOH).