Espalhamento de elétrons por moléculas através de pseudopotenciais "local-density"

Orientadores: Luiz Guimarães Ferreira, Marco Aurelio Pinheiro LimaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Não informadoAbstract: Not informedDoutoradoFísicaDoutor em Ciência

Electron collisions with the HCOOH...(H2O)n (n=1, 2 and 3) complexes in liquid phase: the influence on the π* shape resonance of formic acid

In this conference we report cross sections for elastic collisions of low-energy electrons with the HCOOH…(H2O)n complexes, with n = 1, 2 and 3. The scattering cross sections were computed with the Schwinger multichannel method [K. Takatsuka and V. McKoy, Phys. Rev. A 24 , 2473 (1981); Phys. Rev. A 30 , 1734 (1984)] with pseudopotentials [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47,\ud 1111 (1993)] in the static-exchange and static-exchange plus polarization approximations, for energies from 0.5 eV to 6 eV. We considered some diÆerent hydrogen-bonded structures for the complexes that were generated with classical Monte Carlo simulations [K. Coutinho and S. Canuto, J. Chem. Phys. 113, 9132, (2000)]. The aim of this work is to investigate the effect of the surrounding water molecules on the π* shape resonance of the solute. Previous theoretical and experimental studies carried out in the gas phase reported a π* state for HCOOH at around 1.9 eV. For the n = 1 case and for all complexes, the stabilization of the resonance was observed (it appears at lower energy compared to the value obtained in the gas phase), as reported previously for the CH2O…H2O complexes [T. C. Freitas, M. A. P. Lima, S. Canuto, and M. H. F. Bettega, Phys. Rev. A 80, 062710 (2009)]. This result indicates that the presence of the solvent may affect the processes related to the π* state, such as the molecular dissociation by electron impact. For the n = 2 case we have observed both stabilization and destabilization of the π* resonance, that is associated with the hydrogen bond donor or acceptor role of the water molecules in the complexes. For the n = 3 case, preliminary static-exchange results show the stabilization of the π* state. We propose an explanation of the stabilization/destabilization of the π* state in terms of the polarization of the solute due to the surrounding water molecules and the net charge in the solute.CNPqFINE

Low energy elastic and electronically inelastic electron scattering from biomolecules.

Reactions initiated by collisions with low-energy secondary electrons has been found to be the prominent\ud mechanism toward the radiation damage on living tissues through DNA strand breaks. Now it is widely accepted\ud that during the interaction with these secondary species the selective breaking of chemical bonds is triggered\ud by dissociative electron attachment (DEA), that is, the capture of the incident electron and the formation\ud of temporary negative ion states [1,2,3]. One of the approaches largely used toward a deeper understanding\ud of the radiation damage to DNA is through modeling of DEA with its basic constituents (nucleotide bases,\ud sugar and other subunits). We have tried to simplify this approach and attempt to make it comprehensible\ud at a more fundamental level by looking at even simple molecules. Studies involving organic systems such as\ud carboxylic acids, alcohols and simple ¯ve-membered heterocyclic compounds are taken as starting points for\ud these understanding. In the present study we investigate the role played by elastic scattering and electronic\ud excitation of molecules on electron-driven chemical processes. Special attention is focused on the analysis of\ud the in°uence of polarization and multichannel coupling e®ects on the magnitude of elastic and electronically\ud inelastic cross-sections. Our aim is also to investigate the existence of resonances in the elastic and electronically\ud inelastic channels as well as to characterize them with respect to its type (shape, core-excited or Feshbach),\ud symmetry and position. The relevance of these issues is evaluated within the context of possible applications\ud for the modeling of discharge environments and implications in the understanding of mutagenic rupture of DNA\ud chains. The scattering calculations were carried out with the Schwinger multichannel method (SMC) [4] and\ud its implementation with pseudopotentials (SMCPP) [5] at di®erent levels of approximation for impact energies\ud ranging from 0.5 eV to 30 eV.\ud References\ud [1] B. Boudai®a, P. Cloutier, D. Hunting, M. A. Huels and L. Sanche, Science 287, 1658 (2000). [2] X. Pan, P.\ud Cloutier, D. Hunting and L. Sanche, Phys. Rev. Lett. 90, 208102 (2003). [3] F. Martin, P. D. Burrow, Z. Cai,\ud P. Cloutier, D. Hunting and L. Sanche, Phys. Rev. Lett. 93, 068101 (2004). [4] K. Takatsuka and V. McKoy,\ud Phys. Rev. A 24, 2437 (1981); ibid. Phys. Rev. A 30, 1734 (1984). [5] M. H. F. Bettega, L. G. Ferreira and\ud M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)

Shape Resonance Spectra of Lignocellulose Components.

Replacing fossil fuels for biofuels from renewable sources is a viable way to reduce\ud greenhouse gas emissions. A major goal to optimize biofuel production would be the\ud development of high-yield methods to obtain fermentable sugars from lignocellulosic\ud biomass (leaves, straw, bagasse, etc). This is not an easy task since the biomass is a\ud composite material resistant to chemical or enzymatic hydrolysis.FAPESPCNPqFundação Araucári

Study of elastic scattering of electrons by atoms through pseudopotentials.

Através do uso de pseudopotenciais e possível simplificarmos o calculo de estrutura eletrônica de átomos, moléculas ou sólidos, pois não ha necessidade de incluirmos os orbitais de caroço. Entretanto, tais pseudopotenciais ainda não foram utilizados em cálculos de espalhamento, havendo a necessidade de serem testados. Realizamos um estudo utilizando os pseudopotenciais de Bachelet, Hamann e Schluter em cálculos de espalhamento de elétrons por átomos, calculando phase shifts e seções de choque para momentos angulares 1=0, 1 e 2 com elétrons incidentes possuindo energia ate 5ry. Comparamos os resultados obtidos com o uso dos pseudopotenciais e do potencial de todos os elétrons, os quais se mostraram em ótimo acordo, existindo, porem, restrições na faixa de energia em que os cálculos podem ser realizados. Visamos, desta forma, simplificar o calculo de espalhamento por moléculas complexas.Pseudopotentials allow an extraordinary simplification in the calculation of the electronic structure of atoms, molecules and crystals. Though they have benn used extensively for electronic structure calculations, little is known of their applicability to scattering. We made a study of the pseudopotentials of Bacheket, Hamann and Schlüter in the electron scattering by atoms, calculating phase-shifts and cross sections for angular moments 1=0,1 and energy up to 5Ry. We compare the results for the pseudopotential with the all-electron calculation. The agreement is very good in a broad energy band. We aim at simplifying the calculation of scattering by complex molecules where an all-electron calculation is impossible

Study of elastic scattering of electrons by atoms through pseudopotentials.

Através do uso de pseudopotenciais e possível simplificarmos o calculo de estrutura eletrônica de átomos, moléculas ou sólidos, pois não ha necessidade de incluirmos os orbitais de caroço. Entretanto, tais pseudopotenciais ainda não foram utilizados em cálculos de espalhamento, havendo a necessidade de serem testados. Realizamos um estudo utilizando os pseudopotenciais de Bachelet, Hamann e Schluter em cálculos de espalhamento de elétrons por átomos, calculando phase shifts e seções de choque para momentos angulares 1=0, 1 e 2 com elétrons incidentes possuindo energia ate 5ry. Comparamos os resultados obtidos com o uso dos pseudopotenciais e do potencial de todos os elétrons, os quais se mostraram em ótimo acordo, existindo, porem, restrições na faixa de energia em que os cálculos podem ser realizados. Visamos, desta forma, simplificar o calculo de espalhamento por moléculas complexas.Pseudopotentials allow an extraordinary simplification in the calculation of the electronic structure of atoms, molecules and crystals. Though they have benn used extensively for electronic structure calculations, little is known of their applicability to scattering. We made a study of the pseudopotentials of Bacheket, Hamann and Schlüter in the electron scattering by atoms, calculating phase-shifts and cross sections for angular moments 1=0,1 and energy up to 5Ry. We compare the results for the pseudopotential with the all-electron calculation. The agreement is very good in a broad energy band. We aim at simplifying the calculation of scattering by complex molecules where an all-electron calculation is impossible