The electron-centric approach to the exchange-correlation energy.

The Kohn-Sham theory addresses the challenge of representing the kinetic energy by re-quantizing density functional theory at a level of non-interacting electrons. It transforms the many-electron problem into a fictitious non-interacting electron problem, with the many-electron effects concealed within the exchange-correlation (XC) energy, which is expressed in terms of the electron density ρ(r). Unlike the wave function, ρ(r) can be viewed as a classical quantity, and expressing the XC energy in terms of it circumvents the need for correlated wave functions.

Generating Exchange-Correlation Functionals with a Simplified, Self-Consistent Correlation Factor Model.

We focus on the spherically averaged exchange-correlation hole ρ(, ) of density functional theory, which describes the reduction in the electron density at a distance due to the reference electron localized at position . The correlation factor (CF) approach, where the model exchange hole ρ(, ) is multiplied by a CF ((, )) to yield an approximation to the exchange-correlation hole ρ(, ) = (, ) ρ(, ), has proven to be a powerful tool for the development of new approximations. One of the remaining challenges within the CF approach is the self-consistent implementation of the resulting functionals.

The fourth-order expansion of the exchange hole and neural networks to construct exchange-correlation functionals.

The curvature Q of spherically averaged exchange (X) holes ρ(r, u) is one of the crucial variables for the construction of approximations to the exchange-correlation energy of Kohn-Sham theory, the most prominent example being the Becke-Roussel model [A. D. Becke and M.

The factorization ansatz for non-local approximations to the exchange-correlation hole.

Among the various types of approximations to the exchange-correlation energy (E), the completely non-local approach is one of the lesser explored approximation schemes. It has not yet reached the predictive power of the widely used generalized gradient approximations, meta-generalized gradient approximations, hybrids, etc. In non-local functionals pursued here, the electron density at every point in space is employed to express the exchange-correlation energy per particle ϵ(r) at a given position r.

Constructing and representing exchange-correlation holes through artificial neural networks.

One strategy to construct approximations to the exchange-correlation (XC) energy E of Kohn-Sham density functional theory relies on physical constraints satisfied by the XC hole ρ(r, u). In the XC hole, the reference charge is located at r and u is the electron-electron separation. With mathematical intuition, a given set of physical constraints can be expressed in a formula, yielding an approximation to ρ(r, u) and the corresponding E.

The correlation factor approach: Combining density functional and wave function theory.

Several of the limitations of approximate exchange-correlation functionals within Kohn-Sham density functional theory can be eliminated by extending the single-determinant reference system to a multi-determinant one. Here, we employ the correlation factor ansatz to combine multi-configurational, self-consistent field (MCSCF) with approximate density functionals. In the proposed correlation factor approach, the exchange-correlation hole ρ(r, u), a function of the reference point r and the electron-electron separation u, is written as a product of the correlation factor f(r, u) and an exchange plus static-correlation hole ρ(r, u), i.

Characterization factors for terrestrial acidification at the global scale: a systematic analysis of spatial variability and uncertainty.

Characterization factors (CFs) are used in life cycle assessment (LCA) to quantify the potential impact per unit of emission. CFs are obtained from a characterization model which assess the environmental mechanisms along the cause-effect chain linking an emission to its potential damage on a given area of protection, such as loss in ecosystem quality. Up to now, CFs for acidifying emissions did not cover the global scale and were only representative of their characterization model geographical scope.

Life cycle impact assessment of terrestrial acidification: modeling spatially explicit soil sensitivity at the global scale.

This paper presents a novel life cycle impact assessment (LCIA) approach to derive spatially explicit soil sensitivity indicators for terrestrial acidification. This global approach is compatible with a subsequent damage assessment, making it possible to consistently link the developed midpoint indicators with a later endpoint assessment along the cause-effect chain-a prerequisite in LCIA. Four different soil chemical indicators were preselected to evaluate sensitivity factors (SFs) for regional receiving environments at the global scale, namely the base cations to aluminum ratio, aluminum to calcium ratio, pH, and aluminum concentration.

Development of normalization factors for Canada and the United States and comparison with European factors.

In Life Cycle Assessment (LCA), normalization calculates the magnitude of an impact (midpoint or endpoint) relative to the total effect of a given reference. The goal of this work is to calculate normalization factors for Canada and the US and to compare them with existing European normalization factors. The differences between geographical areas were highlighted by identifying and comparing the main contributors to a given impact category in Canada, the US and Europe.

Epidemiology of Crohn's disease in Québec, Canada.

Background: Crohn's disease (CD) is an idiopathic inflammatory bowel disease (IBD). We aimed to determine the prevalence and incidence of CD in Québec and characterize the demographic and health-related factors associated with this disease.

Methods: We identified CD cases in the provincial administrative databases for the years 1993-2002.

Artificial exomuscle investigations for applications--metal hydride.

In pursuing the development of bionic devices, Victhom identified a need for technologies that could replace current motorized systems and be better integrated into the human body motion. The actuators used to obtain large displacements are noisy, heavy, and do not adequately reproduce human muscle behavior. Subsequently, a project at Victhom was devoted to the development of active materials to obtain an artificial exomuscle actuator.