Navegando por Assunto "DFT (Density Functional Theory)"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Design de nanodispositivos eletroluminescentes baseados no ALQ3
(Universidade Federal do Pará, 2013-04-29) SILVA, Alessandre Sampaio da; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
In this study we investigated theoretically the electronic structure of [tris-(8-hidroxiquinolinolato) aluminum (III) - Alq3, solvation properties of the electroluminescent Alq3 organic liquids such as methanol, ethanol, dimethylformamide (DMF) and acetonitrile in order to understand the dependence the variation of system environments, improving the operation of conveyors films in electroluminescent devices of the type OLED (Organic Light-Emitting Diodes), and finally investigated the mechanism of Alq3 in the electron transport applying a low electrical current in the molecule and current curves showing the –voltage characteristic of the device. The simulation method consists of applying the sequential Monte Carlo / Quantum Mechanics (S-MC/MQ), that part of an initial treatment for separation of stochastic structures most likely to lower energy and subsequently with a quantum treatment to plot the electronic spectra of the layers solvation separated by the ZINDOS/S method. In the electrical properties of transport we use the Green function method coupled nonequilibrium density functional theory (DFT) inferring that the ramifications outer rings corresponding to the Alq3 would terminals for electronic transfer. Our results showed that the average absorption spectra of Alq3 for solvation in solutions undergoes a minimum deviation with changing environment, being in good agreement with the experimental results from the literature, and the IV curves confirmed the behavior of the diode device, corroborating the senses as more relevant to the terminals in Alq3 to have a satisfactory transport electronics.
Acesso aberto (Open Access)
. Predição das propriedades termodinâmicas do biodiesel e diesel comum, suas blendas e efeitos de aditivos via teoria do funcional da densidade e ensemble canônico.
(Universidade Federal do Pará, 2019-11-08) ROCHA, Adriano Santos da; CHAVES NETO, Antonio Maia de Jesus; http://lattes.cnpq.br/3507474637884699
In this study, we analyzed the thermodynamic properties of soy biodiesel, the most widely used biodiesel source among the world's largest consumers, and rapeseed biodiesel, a source with significant employment in the European Union and biodiesel additives. Also, the study of ordinary diesel was carried out to simulate the situations in which this fuel is in mixtures with different concentrations of biodiesel blends. The objective of this work is to study the thermodynamic properties of the fuels mentioned. Based, where possible, on experimental results to validate the expansion of theoretical results and point out the most appropriate methodology for this type of approach. To this end, computational simulations were carried out with theoretical support in the Density Functional Theory combined with the canonical ensemble model. The functional used in the simulations was type B3LYP with bases 6-31 + (d) and 6-311 + g (d), in addition to the composite method CBS-QB3. The calculated enthalpy values are higher in the biofuels in relation to diesel and the same happened with Entropy. When we analyze the change of Gibbs Free Energy, the largest variations were noted for biofuels. The coefficient of adiabatic expansion revealed lower degrees of freedom until 400 K temperature in both types of biodiesel, from that point all fuels have the same behavior for this property. The lowest relative error was found with the B3LYP/6-311 +g(d) method, with a value of 0.15% for the combustion of ordinary diesel. In relation to biofuels, the same method provided 0.48% relative error in the combustion of rapeseed biodiesel as the best result. Regarding the effects of temperature on these fuels, the results showed that both types of biodiesel are less susceptible to heating than ordinary diesel at all calculated points, always requiring more energy to raise their temperature. The results in the additives showed that the antioxidant pyrogallol that most interferes in the biodiesel properties.
Acesso aberto (Open Access)
Transporte eletrônico em um alótropo de grafeno nanofitas de bifenileno com bordas hidrogenadas
(Universidade Federal do Pará, 2024-11-06) SOUZA, Lucas Pessoa de; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
Carbon-based nanostructured materials have aroused considerable interest in the scientific community due to their remarkable technological properties. Among the various carbon structures, graphene stands out as an allotropic form with a two-dimensional (2D) hexagonal structure, resulting from the sp² hybridization of carbon. In this work, we investigated the electronic properties of structures based on a 2D allotropic form of carbon, composed of rings of 4, 6 and 8, called Biphenylene. The research used the hydrogenation of the top of Biphenylene nanosheets, with the aim of exploring applications in molecular electronics. To achieve this, we employ Density Functional Theory (DFT) to optimize the structures and combine DFT with the Non-Equilibrium Green Functions method to obtain electronic transport properties. The band structure results indicate that, among the unit cells analyzed, the Biphenylene cell behaves as a conductive material when analyzed in the zigzag direction, while in the archmair direction they present characteristics of semiconductors. Regarding electronic transport properties, the Biphenylene nanodevice demonstrates behaviors like those of a field effect transistor in the studied range. Specifically, the zzBFNRH-O device, which exhibits field-effect transistor characteristics in the range of 0.00 V to 0.07 V, the same behavior we can observe for the zzBFNRH-H device, which exhibits the behavior of a field effect transistor for ranges from 0.00V to 0.50V. We can observe the behavior of the archBFNRH-O device where it indicates the behavior of a metal, presenting current conduction values after 0.10V. The archBFNRH-H device presents the behavior of a semiconductor, which indicates a gap of 1.8eV. We can observe that when the device width increases, this gap decreases. These results demonstrate that structures based on Biphenylene present themselves as a promising alternative for the development of nanodevices and applications in molecular electronics.