Hannover 2016 – scientific programme

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MO: Fachverband Molekülphysik

MO 2: Collisions, Energy transfer and ab initio Modelling

MO 2.5: Talk

Monday, February 29, 2016, 12:00–12:15, f142

Natural extension of Hartree-Fock through extremal 1-fermion information — •Carlos L. Benavides-Riveros — Martin-Luther-Universität Halle-Wittenberg, 06120 Halle (Saale), Germany

Fermionic natural occupation numbers (NON) do not only obey Pauli's exclusion principle but are even stronger restricted by so-called generalized Pauli constraints. Whenever given NON lie on the boundary of the allowed region the corresponding N-fermion quantum state has a significantly simpler structure. By employing this structure a variational optimization method for few fermion ground states is elaborated. We quantitatively confirm its high accuracy for systems with the vector of NON in a small distance to the boundary of the polytope. In particular, we derive an upper bound on the error of the correlation energy given by the ratio of the distance to the boundary of the polytope and the distance of the vector of NON to the Hartree-Fock point. As a consequence, the proposed method is the computationally cheapest covering the leading order correlations for systems exhibiting the recently found quasipinning phenomenon. Moreover, these geometric insights shed some light on the concept of active spaces, correlation energy, frozen electrons and virtual orbitals.