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MM: Fachverband Metall- und Materialphysik
MM 39: Methods in Computational Materials Modelling V: Kinetics and Beyond DFT
MM 39.6: Vortrag
Mittwoch, 18. März 2015, 17:15–17:30, H 0106
Correlation energy in the Adiabatic Connection Fluctuation-Dissipation Theory beyond RPA: Systematic development and simple approximations — •Nicola Colonna1, Maria Hellgren2, and Stefano de Gironcoli3,4 — 1Theory and Simulation of Materials (THEOS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland — 2Physics and Materials Science, University of Luxembourg, L-1511 Luxembourg, Luxembourg — 3International School for Advanced Studies (SISSA), I-34136 Trieste, Italy — 4CNR-IOM Democritos, I-34136 Trieste, Italy
We present a systematic approach to compute accurate correlation energies in the adiabatic connection fluctuation dissipation (ACFD) framework beyond RPA. To first order our scheme leads to the RPA plus exact-exchange kernel (RPAx), for which a novel and efficient implementation is proposed. It is based on an eigenvalue decomposition of the time dependent response function of the Many Body system in the limit of vanishing coupling constant, evaluated by density functional perturbation theory. The accuracy of the RPAx approximation has been tested calculating the correlation energy of the homogeneous electron gas and studying the dissociation energy curves of selected diatomic molecules. A sensible improvement of the total energy description is disturbed by a pathological behavior of the response function. Staying within an exact first-order approximation to the response function, we use an alternative resummation of the higher-order terms. This slight redefinition of RPAx fixes the instability in total energy calculations without compromising the overall accuracy of the approach.