Efficient dielectric matrix calculations using the Lanczos algorithm for fast many-body G0W0G_0W_0 implementations

We present a $G_0W_0$ implementation that assesses the two major bottlenecks of traditional plane-waves implementations, the summations over conduction states and the inversion of the dielectric matrix, without introducing new approximations in the formalism. The first bottleneck is circumvented by converting the summations into Sternheimer equations. Then, the novel avenue of expressing the dielectric matrix in a Lanczos basis is developed, which reduces the matrix size by orders of magnitude while being computationally efficient. We also develop a model dielectric operator that allows us to further reduce the size of the dielectric matrix without accuracy loss. Furthermore, we develop a scheme that reduces the numerical cost of the contour deformation technique to the level of the lightest plasmon pole model. Finally, the use of the simplified quasi-minimal residual scheme in replacement of the conjugate gradients algorithm allows a direct evaluation of the $G_0W_0$ corrections at the desired real frequencies, without need for analytical continuation. The performance of the resulting $G_0W_0$ implementation is demonstrated by comparison with a traditional plane-waves implementation, which reveals a 500-fold speedup for the silane molecule. Finally, the accuracy of our $G_0W_0$ implementation is demonstrated by comparison with other $G_0W_0$ calculations and experimental results.Comment: 19 pages, 2 figure

Considérations en provenance de Sirius

Afin de mesurer l’impact de la musique de Stockhausen sur la musique actuelle, ce courant protéiforme de musique improvisée, qui absorbe si facilement des influences tant savantes que populaires, le musicien et compositeur Michel F. Côté se penche sur la question, et s’y greffant les propos d’autres illustres musiciens associés à ce courant tels le saxophoniste Jean Derome et le turntablist Martin Tétreault.To gauge the impact of Stockhausen on the “musique actuelle” scene, that Protean form of improvised music which so easily absorbs learned as well as popular traditions, the musician and composer Michel F. Côté examines the question, and draws on other well-known musicians associated with this genre, including the saxophonist Jean Derome and the turntablist Martin Tétreault

Explaining Sales Pay Strategy Using Agency, Transaction Cost and Resource Dependence Theories

The purpose of this study was to investigate, using data gathered from 325 French-Canadian organizations, the influence of key constructs related to agency, transaction cost and resource dependence theories on the proportion of salary in sales compensation. Level of task programmability, capacity to observe behavior, career opportunities and financial resources offered were associated with an increased use of salary pay. In contrast, difficulty of measuring result outcomes, availability of product/service-related resources and high marginal sales force productivity were associated with decreased use of the salary component. Results supported the argument that integration of multiple theoretical perspectives offered a better explanation of pay policy. However, the results have not supported the ability of market and selling uncertainty to predict the proportion of salary L'objectif de cette étude était d'examiner, auprès d'un échantillon de 325 organisations, l'influence des construits clés relatifs à la théorie de l'agence, la théorie des coûts de transaction et la théorie de la dépendence des ressource sur la proportion du salaire dans l'enveloppe de la rémunération directe du personnel de vente. Le niveau de programmation des tâches, la capacité à observer les comportements, les opportunités de carrière et les ressources financières offertes étaient associés à une augmentation du recours de la composante salariale. En revanche, le degré de difficulté à mesurer les résultats, la disponibilité de ressources reliés aux produits/services et un grand différentiel de performance étaient associés à une diminution de la composante salaire. Les résultats supportent l'argument de l'intégration d'une multitude de perspecttives théoriques pour expliquer le choix des stratégies salariales.Sales, compensation, agency theory, cost analysis theory, resource dependence theory, Représentants aux ventes, rémunération, théorie de l'agence, théorie des coûts de transaction, théorie de la dépendance des ressources

DFT+U study of magnetic order in doped La2_2CuO4_4 crystals

This article presents the results of several magnetic phases of doped La$_{2-x}$Sr$_x$CuO$_4$ using density-functional theory with an added Hubbard term (DFT+U). Doping factors from $x=0$ to 0.25 were examined. We found that a bond centered stripe is the magnetic ground state for $x=1/8$ and $x=1/4$. No stable stripe order was found for $x=1/6$. Analysis of the electron density revealed that apical oxygen atoms, those located above and below the copper atoms in the CuO$_2$ planes, hold a non negligible part of the holes at large doping and present a small spin polarization. Finally, the charge reorganization caused by the magnetic stripe modulation was studied for bond centered and atom centered stripes.Comment: 7 pages, 6 figures (submitted to PRB

Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the electronic structure

The renormalization of the band structure at zero temperature due to electron-phonon coupling is investigated in diamond, BN, LiF and MgO crystals. We implement a dynamical scheme to compute the frequency-dependent self-energy and the resulting quasiparticle electronic structure. Our calculations reveal the presence of a satellite band below the Fermi level of LiF and MgO. We show that the renormalization factor (Z), which is neglected in the adiabatic approximation, can reduce the zero-point renormalization (ZPR) by as much as 40%. Anharmonic effects in the renormalized eigenvalues at finite atomic displacements are explored with the frozen-phonon method. We use a non-perturbative expression for the ZPR, going beyond the Allen-Heine-Cardona theory. Our results indicate that high-order electron-phonon coupling terms contribute significantly to the zero-point renormalization for certain materials