Prediction of the derivative discontinuity in density functional theory from an electrostatic description of the exchange and correlation potential

We propose a new approach to approximate the exchange and correlation (XC) functional in density functional theory. The XC potential is considered as an electrostatic potential, generated by a fictitious XC density, which is in turn a functional of the electronic density. We apply the approach to develop a correction scheme that fixes the asymptotic behavior of any approximated XC potential for finite systems. Additionally, the correction procedure gives the value of the derivative discontinuity; therefore it can directly predict the fundamental gap as a ground-state property.Comment: 5 pages, 4 figure

Non-local modelling of ductile damage : formulation and numerical issues

Tese de doutoramento. Engenharia Mecânica. Universidade do Porto. Faculdade de Engenharia. 201

Real-Space Density Functional Theory on Graphical Processing Units: Computational Approach and Comparison to Gaussian Basis Set Methods

We discuss the application of graphical processing units (GPUs) to accelerate real-space density functional theory (DFT) calculations. To make our implementation efficient, we have developed a scheme to expose the data parallelism available in the DFT approach; this is applied to the different procedures required for a real-space DFT calculation. We present results for current-generation GPUs from AMD and Nvidia, which show that our scheme, implemented in the free code Octopus, can reach a sustained performance of up to 90 GFlops for a single GPU, representing a significant speed-up when compared to the CPU version of the code. Moreover, for some systems our implementation can outperform a GPU Gaussian basis set code, showing that the real-space approach is a competitive alternative for DFT simulations on GPUs.Chemistry and Chemical Biolog

Robust design of a passive wind turbine system

The effectiveness of full passive Wind Turbine (WT) systems has been recently demonstrated. Such low cost and reliable structures without active control and with a minimum number of sensors can be efficient only if the system design parameters are mutually adapted through an integrated optimal design approach. Even if there is a good agreement between theoretical design models and an experimental prototype, it is relevant to evaluate the WT efficiency with respect to design variable variations. Thus, this work is devoted more specifically to the sensitivity analysis of a passive WT system according to electrical variable variations of the Permanent Magnet Synchronous Generator (PMSG). It also investigates the interest of a robust design approach for reducing the sensitivity of the WT efficiency to specific variable variations

More Electricity in the Air: Toward Optimized Electrical Networks Embedded in More-Electrical Aircraft.

Along with the main trends and future challenges of electrical networks embedded in more-electrical aircraft, this article also focuses on optimization efforts in the field of industrial electronics and energy conversion. Optimization can be achieved by the means of expertise or from classical analysis methods, especially those based on simulations. However, novel approaches based on optimization algorithms, so-called integrated design by optimization, are becoming increasingly mature and will become particularly powerful if subsequent efforts are made in terms of modeling for design. In the first part, the current context and new standards of the more-electrical aircraft are summarized. The second part deals with the new trends and challenges of more electrical aircraft, with an emphasis on reversible and hybrid high-voltage dc networks including new storage devices. However, this discussion will mainly focus on systems optimization. Methodological orientations toward integrated optimal design are discussed with representative examples, such as for an environmental conditioning system (ECS)

Identification of Orthotropic Elastic Properties of Wood by a Synthetic Image Approach Based on Digital Image Correlation

No 888153 CENTRO-01-0145-FEDER-029713 POCI-01-0145-FEDER-031243 POCI-01-0145-FEDER-030592 ENTRO-01-0145-FEDER-022083This work aims to determine the orthotropic linear elastic constitutive parameters of Pinus pinaster Ait. wood from a single uniaxial compressive experimental test, under quasi-static loading conditions, based on two different specimen configurations: (a) on-axis rectangular specimens oriented on the radial-tangential plane, (b) off-axis specimens with a grain angle of about 60◦ (radial-tangential plane). Using digital image correlation (DIC), full-field displacement and strain maps are obtained and used to identify the four orthotropic elastic parameters using the finite element model updating (FEMU) technique. Based on the FE data, a synthetic image reconstruction approach is proposed by coupling the inverse identification method with synthetically deformed images, which are then processed by DIC and compared with the experimental results. The proposed methodology is first validated by employing a DIC-levelled FEA reference in the identification procedure. The impact of the DIC setting parameters on the identification results is systematically investigated. This influence appears to be stronger when the parameter is less sensitive to the experimental setup used. When using on-axis specimen configuration, three orthotropic parameters of Pinus pinaster (ER, ET and νRT ) are correctly identified, while the shear modulus (GRT ) is robustly identified when using off-axis specimen configuration.publishersversionpublishe

A time-dependent density functional theory scheme for efficient calculations of dynamic (hyper)polarizabilities

We present an efficient perturbative method to obtain both static and dynamic polarizabilities and hyperpolarizabilities of complex electronic systems. This approach is based on the solution of a frequency dependent Sternheimer equation, within the formalism of time-dependent density functional theory, and allows the calculation of the response both in resonance and out of resonance. Furthermore, the excellent scaling with the number of atoms opens the way to the investigation of response properties of very large molecular systems. To demonstrate the capabilities of this method, we implemented it in a real-space (basis-set free) code, and applied it to benchmark molecules, namely CO, H2O, and paranitroaniline (PNA). Our results are in agreement with experimental and previous theoretical studies, and fully validate our approach.Comment: 9 pages, 4 figure

Application of Compressed Sensing to the Simulation of Atomic Systems

Compressed sensing is a method that allows a significant reduction in the number of samples required for accurate measurements in many applications in experimental sciences and engineering. In this work, we show that compressed sensing can also be used to speed up numerical simulations. We apply compressed sensing to extract information from the real-time simulation of atomic and molecular systems, including electronic and nuclear dynamics. We find that, compared to the standard discrete Fourier transform approach, for the calculation of vibrational and optical spectra the total propagation time, and hence the computational cost, can be reduced by approximately a factor of five.Chemistry and Chemical Biolog