Objectif
Quantum chemistry provides two approaches to molecular electronic-structure calculations: the systematically refinable but expensive many-body wave-function methods and the inexpensive but not systematically refinable Kohn Sham method of density-functional theory (DFT). The accuracy of Kohn Sham calculations is determined by the quality of the exchange correlation functional, from which the effects of exchange and correlation among the electrons are extracted using the density rather than the wave function. However, the exact exchange correlation functional is unknown—instead, many approximate forms have been developed, by fitting to experimental data or by satisfying exact relations. Here, a new approach to density-functional analysis and construction is proposed: the Lieb variation principle, usually regarded as conceptually important but impracticable. By invoking the Lieb principle, it becomes possible to approach the development of approximate functionals in a novel manner, being directly guided by the behaviour of exact functional, accurately calculated for a wide variety of chemical systems. In particular, this principle will be used to calculate ab-initio adiabatic connection curves, studying the exchange correlation functional for a fixed density as the electronic interactions are turned on from zero to one. Pilot calculations have indicated the feasibility of this approach in simple cases—here, a comprehensive set of adiabatic-connection curves will be generated and utilized for calibration, construction, and analysis of density functionals, the objective being to produce improved functionals for Kohn Sham calculations by modelling or fitting such curves. The ABACUS approach will be particularly important in cases where little experimental information is available—for example, for understanding and modelling the behaviour of the exchange correlation functional in electromagnetic fields.
Champ scientifique
Appel à propositions
ERC-2010-AdG_20100224
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Régime de financement
ERC-AG - ERC Advanced GrantInstitution d’accueil
0313 Oslo
Norvège