Analysis of the contributions of three-body potentials in the equation of state of 4He

The effect of three-body interatomic contributions in the equation of state of 4He are investigated. A recent two-body potential together with the Cohen and Murrell (Chem. Phys. Lett. 260, 371 (1996)) three-body potential are applied to describe bulk helium. The triple-dipole dispersion and exchange energies are evaluated subjected only to statistical uncertainties. An extension of the diffusion Monte Carlo method is applied in order to compute very small energies differences. The results show how the three-body contributions affects the ground-state energy, the equilibrium, melting and freezing densities.Comment: 18 pages, 3 figures, 4 table

Análise de potenciais de interação nos sistemas de átomos de hélio

Orientador: Silvio Antonio Sachetto VitielloTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Na primeira parte da tese, os efeitos das contribuições interatômicas de três corpos na equação de estado do 4 He são investigadas. Um potencial recente de dois corpos junto com o potencial de três corpos de Cohen e Murrell são utilizados para descrever o sistema de átomos de hélio. A dispersão de triplo dipolo e as energias de troca são estimadas sujeitas só a incertezas estatísticas. Uma extensão ao método de difusão com Monte Carlo é empregado para calcular diferenças de energias muito pequenas. Os resultados mostram como as contribuições de três corpos afetam a energia do estado fundamental, e as densidades de equilíbrio, solidificação e liquefação. Na investigação dos sistemas de hélio, diversos potenciais ab initio de dois corpos foram propostos na literatura. Nesta segunda parte da tese realizamos uma análise cuidadosa de como estes potenciais descrevem as propriedades do sistemas de 4 He usando a extensão proposta ao método de difusão com Monte Carlo. Esta extensão nos permitiu calcular com grande precisão pequenas diferenças de energia associadas a diferentes potenciais como função da densidade do sistema. Com estes resultados foi possível acompanhar cuidadosamente como a descrição das propriedades do sistema mudam com os potenciais de dois corpos considerados. Da nossa análise identificamos o potencial que em conjunto com interações de três corpos foi capaz de fornecer a melhor descrição dos sistemas de hélioAbstract: In the first part of the thesis, the effect of three-body interatomic contributions in the equation of state of 4 He are investigated. A recent two-body potential together with the Cohen and Murrell three-body potential are applied to describe the sistem of helium atoms. The triple dipole dispersion and exchange energies are evaluated subjected only to statistical uncertainties. An extension of the diffusion Monte Carlo method is applied in order to compute very small energies differences. The results show how the three-body contributions affects the ground-state energy, the equilibrium, melting and freezing densities. In the investigation of the helium systems several ab initio two-body potentials have been propoused in the literature. In the second part of the thesis, we performed a carefull analysis of how these potentials describe the properties of the 4 He systems by using the proposed extension to the diffusion Monte Carlo Method. This extension have allowed the calculation of small energies differences, due to the different potentials, as a function of the system density with great accuracy. With our results it is possible to carefully follow how properties of the sistem change with the two-body potentials considered. From our analises we identify the potential that together with three-body interactions is able to give the best description of the helium systemsDoutoradoFísicaDoutor em Ciência

Solid He-4 and the diffusion Monte Carlo method: a study of their properties

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQProperties of helium atoms in the solid phase are investigated using the multiweight diffusion Monte Carlo method. Two different importance function transformations are used in two series of independent calculations. The kinetic energy is estimated for both the solid and liquid phases of He-4. We estimate the melting and freezing densities, among other properties of interest. Our estimates are compared with experimental values. We discuss why walkers biased by two distinctly different guiding functions do not lead to noticeable changes in the reported results. Criticisms concerning the bias introduced into our estimates by population control and system size effects are considered.964110FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQSem informaçãoSem informaçãoSem informaçãoThe authors acknowledge financial support from the Brazilian agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Fundação de Amparo à Pesquisa do Estado de Rio de Janeiro (FAPERJ), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). Part of the computations were performed at the Centro Nacional de Processamento de Alto Desempenho em São Paulo (CENAPAD-SP), a high-performance computing facility at Universidade Estadual de Campinas

Visualization of wave function of quantum dot at fermi-edge singularity regime

We consider electron tunneling spectroscopy through an InAs quantum dot in a magnetic field applied perpendicular to the tunneling direction. We examine in details the anisotropic behavior of the amplitude and shape of the resonant peaks of I-V curves and concluded that (i) magnetotunneling spectroscopy at FES regime allows establishing position of resonant level in QD with high accuracy. (ii) The distinguishable shape of FES peak allows extracting the amplitude with much better accuracy. (iii) FES exponent dependence on magnetic field gives additional information about potential distribution outside QD.Foundation for Science and Technology (FCT

Cyclotron enhancement of tunneling

A state of an electron in a quantum wire or a thin film becomes metastable, when a static electric field is applied perpendicular to the wire direction or the film surface. The state decays via tunneling through the created potential barrier. An additionally applied magnetic field, perpendicular to the electric field, can increase the tunneling decay rate for many orders of magnitude. This happens, when the state in the wire or the film has a velocity perpendicular to the magnetic field. According to the cyclotron effect, the velocity rotates under the barrier and becomes more aligned with the direction of tunneling. This mechanism can be called cyclotron enhancement of tunneling

First Principle Calculation of Potential and Multi-Channel Transport in Fe/MgO/Fe Hetero-Junction

In this work we studied the behavior of multi-channel tunneling through a realistic Fe/MgO/Fe hetero-junction ab initio potential. For this purpose we obtained Fe/MgO/Fe(001) hetero-junction effective potentials using the full potential-linear augmented plane wave WIEN2k code together with the generalized gradient approximation for the exchange-correlation potential. Multi-channel tunneling through the Fe/MgO/Fe hetero-junction barrier was studied within a few modes model. The transfer matrix technique was used to calculate the transmission and reflection amplitudes between Bloch states in the semi-infinite leads. The transmission coefficients were used in Fisher and Lee formula for conductance, an expression derived from Kubo formula and valid for any number of scattering channels