Alessandra F. Albernaz

Interactions of Hydrogen Molecules with Halogen-Containing Diatomics from Ab Initio Calculations: Spherical-Harmonics Representation and Characterization of the Intermolecular Potentials

For the prototypical diatomic-molecule-diatomic-molecule interactions H2-HX and H2-X2, where X = F, Cl, Br, quantum-chemical ab initio calculations are carried out on grids of the configuration space, which permit a spherical-harmonics representation of the potential energy surfaces (PESs). Dimer geometries are considered for sets of representative leading configurations, and the PESs are analyzed in terms of isotropic and anisotropic contributions. The leading configurations are individuated by selecting a minimal set of mutual orientations of molecules needed to build the spherical-harmonic expansion on geometrical and symmetry grounds. The terms of the PESs corresponding to repulsive and bonding dimer geometries and the averaged isotropic term, for each pair of interacting molecules, are compared with representations in terms of a potential function proposed by Pirani et al. (see Chem. Phys. Lett. 2004, 394, 37-44 and references therein). Connections of the involved parameters with molecular properties provide insight into the nature of the interactions.

Rovibrational energy and spectroscopic constant calculations of CH 4 ⋯ CH 4, CH 4 ⋯ H 2 O, CH 4 ⋯ CHF 3, and H 2 O ⋯ CHF 3 dimers

In this work, we performed a thorough investigation of potential energy curves, rovibrational spectra, and spectroscopic constants for dimers whose interactions are mediated by hydrogen bonds and other hydrogen interactions. Particularly, we deal with CH 4 ⋯ CH4, CH 4 ⋯ H2 O, CH 4 ⋯ CHF3, and H 2O ⋯ CHF3 dimers by employing accurate electronic energy calculations with two different basis sets at the MP2 level of theory. Following this, the discrete variable representation method was applied to solve the nuclear Schrödinger equation, thus obtaining spectroscopic constants and rovibrational spectra. The harmonic constant, ωe, presents a direct relation to the strength of dimer interactions. As a general rule, it was found that a decrease of interatomic distances is followed by the increase of De for all dimers. This behavior suggests that the interaction of CH 4 ⋯ CH4 is the weakest among all dimers, followed by CH 4 ⋯ CHF3, CH 4 ⋯ H2 O and the strongest interaction given by the H 2O ⋯ CHF3 dimer.

Spherical and hyperspherical harmonics representation of van der Waals aggregates

The representation of the potential energy surfaces of atom molecule or molecular dimers interactions should account faithfully for the symmetry properties of the systems, preserving at the same time a compact analytical form. To this aim, the choice of a proper set of coordinates is a necessary precondition. Here we illustrate a description in terms of hyperspherical coordinates and the expansion of the intermolecular interaction energy in terms of hypersherical harmonics, as a general method for building potential energy surfaces suitable for molecular dynamics simulations of van der Waals aggregates. Examples for the prototypical case diatomic molecule diatomic molecule interactions are shown.

Potential Energy Surface for the Interaction of Helium with the Chiral Molecule Propylene Oxide

The discovery of propylene oxide in the interstellar medium has raised considerable interest about this molecule, which represents one of the simplest cases of chiral systems. In this paper, we present a quantum chemical study and a phenomenological approach, through the Pirani potential function, of the system He – propylene oxide in fourteen different configurations. Comparison of the optimized molecular structure at various level of theory, as well as a discussion on the two approaches is reported. The analytical form of the Pirani potential function permits future applications of classical simulations of molecular-beam collision experiments, especially to those related to chirality discrimination phenomena, in progress in our laboratory.

The spherical-harmonics representation for the interaction between diatomic molecules: The general case and applications to COCO and COHF

Abstract The spherical-harmonics expansion is a mathematically rigorous procedure and a powerful tool for the representation of potential energy surfaces of interacting molecular systems, determining their spectroscopic and dynamical properties, specifically in van der Waals clusters, with applications also to classical and quantum molecular dynamics simulations. The technique consists in the construction (by ab initio or semiempirical methods) of the expanded potential interaction up to terms that provide the generation of a number of leading configurations sufficient to account for faithful geometrical representations. This paper reports the full general description of the method of the spherical-harmonics expansion as applied to diatomic-molecule – diatomic-molecule systems of increasing complexity: the presentation of the mathematical background is given for providing both the application to the prototypical cases considered previously (O2 O2, N2 N2, and N2 O2 systems) and the generalization to: (i) the CO CO system, where a characteristic feature is the lower symmetry order with respect to the cases studied before, requiring a larger number of expansion terms necessary to adequately represent the potential energy surface; and (ii) the CO HF system, which exhibits the lowest order of symmetry among this class of aggregates and therefore the highest number of leading configurations.

Theoretical study of the H + HCN → H + HNC process

AbstractWe present a theoretical study on the detailed mechanism and kinetics of the H+HCN →H+HNC process. The potential energy surface was calculated at the complete basis set quantum chemical method, CBS-QB3. The vibrational frequencies and geometries for four isomers (H2CN, cis-HCNH, trans-HCNH, CNH2), and seven saddle points (TSn where n = 1 − 7) are very important and must be considered during the process of formation of the HNC in the reaction were calculated at the B3LYP/6-311G(2d,d,p) level, within CBS-QB3 method. Three different pathways (PW1, PW2, and PW3) were analyzed and the results from the potential energy surface calculations were used to solve the master equation. The results were employed to calculate the thermal rate constant and pathways branching ratio of the title reaction over the temperature range of 300 up to 3000 K. The rate constants for reaction H + HCN → H + HNC were fitted by the modified Arrhenius expressions. Our calculations indicate that the formation of the HNC preferentially occurs via formation of cis–HCNH, the fitted expression is kPW2(T) = 9.98 × 10−22T2.41 exp(−7.62 kcal.mol−1/RT) while the predicted overall rate constant kOverall(T) = 9.45 × 10−21T2.15 exp(−8.56 kcal.mol−1/RT) in cm3 molecule−1s−1. Graphical Abstract(a) Potential energy surface, (b) thermal rate constants as a function of temperature and (c) the branching ratios (%) of PW1, PW2, PW3 pathways involved in rm H + HCN → H + HNC process.

Estudos Teóricos de Oligômeros Aplicados na Composição de Células Fotovoltaicas ou Diodos Orgânicos Emissores de Luz

Os semicondutores orgânicos foram descobertos ha mais de um seculo, mas somente nos ultimos 30 anos, eles se tornaram o centro das atencoes da industria e academia, devido ao grande potencial de aplicacoes em novos dispositivos tais como os Diodos Orgânicos de Emissao de Luz (OLEDs) e Celulas Fotovoltaicas Orgânicas (OPVs). Neste trabalho, determinamos as geometrias de equilibrio, os gaps de energia, potenciais de ionizacao, eletroafinidades, funcoes trabalho e comprimentos de onda para dez oligomeros (comumente usados na eletronica orgânica) usando os niveis B3LYP/6-31G(d,p)//AM1 e B3LYP/6-31G(d,p). Atraves da analise dessas propriedades, verificamos quais sao os melhores oligomeros para se construir dispositivos OPVs e OLEDs. DOI: 10.5935/1984-6835.20160033

Theoretical Studies of Oligomers Used in the Composition of Photovoltaic Cells or Organic Lighting Emitting Diodes

Organic semiconductors were discovered more than one century ago but only in the past 30 years they have attracted the attention of both academy and industry due to their potential applications in new devices such as Organic Lighting Emitting Diodes (OLEDs) and Organic Photovoltaics (OPVs). In this work, we determined the equilibrium geometries, energy gap, ionization potentials, electron affinities, work function and wavelength of ten oligomers (commonly used in organic electronics) using B3LYP/6-31G(d,p)//AM1 and B3LYP/6-31G(d,p) levels. Through the analysis of electrical properties, we found which oligomers are the best for building OPVs and OLEDs devices.

Previsão de Novos Canais de Reação para o CN + C2H2

Neste trabalho, apresentamos um estudo da reacao do ciano (CN) com a molecula C 2 H 2 . Mais precisamente, determinamos as geometrias, frequencias e energias eletronicas para as diferentes especies envolvidas nos caminhos de reacao do processo CN + C 2 H 2 usando o nivel de calculo M06L/ 6-311++G(d,p). A partir deste estudo, foi possivel propor tres novos caminhos de reacao para este importante processo colisional. DOI: 10.5935/1984-6835.20160038

Hyperspherical Coordinate Potential Energy Surface for the He3Complex

In this work, we show a new Potential Energy Surface (PES) for the He3 complex. The PES was obtained using hyperspherical coordinates. The potential employed has a well defined and very simple analytical form. The radial dependence was obtained by considering three leading configurations whose energies, computed at CCSD(T) and MRCI levels and six different basis sets (aug-cc-pVXZ (X=D,T,Q,5,6) and d-aug-cc-pVQZ), were fitted by a Rydberg function.