Conception assistée par ordinateur pour l'électronique

La CAO électronique (pour Conception assistée par ordinateur électronique), nommée également en anglais EDA (pour Electronic design automation), est la catégorie des outils servant à la conception et la production des systèmes électroniques allant des circuits imprimés jusqu'aux circuits intégrés. Terminologie Le terme CAO est aussi utilisé pour désigner la CAO mécanique, la conception assistée par ordinateur et la fabrication assistée par ordinateur en électronique et en électrotechnique. L'usage de ce terme est probablement dû au comité de conception à l'automatisation technique de l'IEEE. Dans le secteur industriel, ce sont les concepteurs de circuits électroniques des entreprises de semi-conducteurs qui utilisent la CAO. Les grands circuits sont trop complexes pour être conçus à la main et nécessitent des outils informatiques adéquats. Développement de la CAO La CAO a rapidement gagné en importance avec la miniaturisation continuelle de la technologie des

Proving non-termination

Ashutosh Kumar Gupta, Andrey Rybalchenko

The search for proof and the search for counterexamples (bugs) are complementary activities that need to be pursued concurrently in order to maximize the practical success rate of verification tools. While this is well-understood in safety verification, the current focus of liveness verification has been almost exclusively on the search for termination proofs. A counterexample to termination is an infinite program execution. In this paper, we propose a method to search for such counterexamples. The search proceeds in two phases. We first dynamically enumerate lasso-shaped candidate paths for counterexamples, and then statically prove their feasibility. We illustrate the utility of our nontermination prover, called TNT, on several nontrivial examples, some of which require bit-level reasoning about integer representations.

2008

Spectral properties of extended systems from Koopmans-compliant functionals

Riccardo De Gennaro

Electronic-structure simulations have been impacting the study of materials properties thanks to the simplicity of density-functional theory, a method that gives access to the ground state of the system. Although very important, ground-state properties represent just part of the information, and often technological applications rely more on excited-state properties. In the context of density-functional theory, the latter are difficult to extract and one usually has to resort to more sophisticated approaches. In the last years, Koopmans spectral functionals have emerged as an effective method which combines the feasibility of density-functional theory with the accuracy of more complex methods, such as many-body perturbation theory. While retaining its simplicity, Koopmans functionals extend the domain of density-functional theory providing direct access to charged excitations, and ultimately to the photoemission spectra of materials. This approach has been extensively employed in finite systems, displaying an accuracy which is comparable to that of state-of-the-art many-body perturbation theory methods. In extended systems, calculations were bound to the supercell (Gamma-only) method, preventing the access to the full band structure of the system. In this work we overcome this limitation, proving that a band structure description of the energy spectrum is possible, and providing a scheme to carry out calculations in crystalline materials. The first result of this work consists in proving the compliance of Koopmans functionals with the translation symmetry of the system. The validity of Bloch's theorem, thus the possibility of describing the spectrum via a band structure picture, depends on this condition. Because of the orbital-density-dependent nature of the functional, the invariance of the total energy with respect to unitary transformations of the one-electron orbitals is broken. The energy is then minimized by a particular set of orbitals, called ``variational'', which are strongly localized in space. In extended periodic systems, the localized, thus non-periodic, character of the variational orbitals is inherited by the effective orbital-density-dependent Hamiltonians, which apparently break the translation symmetry of the system. Here we show that, by requiring the variational orbitals to be Wannier functions, the translation symmetry is preserved and Bloch's theorem holds. In the second part, we devise a scheme to unfold the band structure from supercell (Gamma-only) calculations, and reconstruct the k-dependence of the quasiparticle energies. This method is then used to compute the band structures of a set of benchmark semiconductors and insulators. Finally, we describe a novel formulation of Koopmans functionals for extended periodic systems, which exploits from the beginning the translation properties of Wannier functions to realize a primitive cell-based implementation of Koopmans functionals. Results obtained from this second approach are also discussed. In the last part, we present the preliminary study of impurity states arising in crystalline materials in the presence of point defects.

EPFL2022

Spectral properties of extended systems from Koopmans-compliant functionals

Riccardo De Gennaro

EPFL2022

Conception assistée par ordinateur pour l'électronique

Proving non-termination

An Approach For Easy Handling And Interchanging Of Large VHDL-Based Design Databases For Simulation And Synthesis

Spectral properties of extended systems from Koopmans-compliant functionals

An Approach For Easy Handling And Interchanging Of Large VHDL-Based Design Databases For Simulation And Synthesis

Proving non-termination

Spectral properties of extended systems from Koopmans-compliant functionals