title: Correlation-Driven Charge and Spin Fluctuations in LaCoO_{3}.
abstract: The spin transition in LaCoO_{3} has been investigated using density-functional theory in combination with dynamical mean-field theory employing continuous time quantum Monte Carlo and exact diagonalization impurity solvers. Calculations on the experimental rhombohedral atomic structure with two Co sites per unit cell show that an independent treatment of the Co atoms results in a ground state with strong charge fluctuations induced by electronic correlations. Each atom shows a contribution from either a d^{5} or a d^{7} state in addition to the main d^{6} state. These states play a relevant role in the spin transition which can be understood as a low spin-high spin (LS-HS) transition with significant contributions (~10%) to the LS and HS states of d^{5} and d^{7} states, respectively. We report spectra as well as optical conductivity data for all cases. A thermodynamic analysis reveals a significant kinetic energy gain through introduction of charge fluctuations, which in addition to the potential energy reduction lowers the total energy of the system.
authors.affiliation: Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Karolak
authors.affiliation: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.|I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany.|Synchrotron Soleil, L'Orme des Merisiers St-Aubin, BP-48, 91192 Gif-sur-Yvette, France.
authors.forename: M
authors.initials: M
authors.lastname: Izquierdo
authors.affiliation: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.|Institute of Experimental Physics, Technische Universität Bergakademie Freiberg, 09599 Freiberg, Germany.|ITMO University, Kronverkskiy prospekt 49, 197101 St. Petersburg, Russia.
authors.forename: S L
authors.initials: SL
authors.lastname: Molodtsov
authors.affiliation: European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.|I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany.
authors.forename: A I
authors.initials: AI
authors.lastname: Lichtenstein