Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 39: Focussed session: Frontiers of electronic structure theory: Strong correlations from first principles III (jointly with TT)

O 39.7: Vortrag

Mittwoch, 28. März 2012, 12:00–12:15, HE 101

Computing the magneto-electric coupling between atoms with numerous open-shells to experimental accuracy : YMnO₃ — •Marie-Bernadette Lepetit — CRISMAT UMR6508 CNRS-ENSICAEN, 6 bd Maréchal Juin, 14050 Caen, FRANCE

In strongly correlated systems the electron-electron repulsion between the Fermi level electrons is of larger magnitude than the kinetic energy. It results that the nature of the ground and the low-lying excited-states is thus fundamentally multi-configurational and single-determinant based methods (such as density functional theory) encounter difficulties in properly describing their electronic structure and more specifically their magnetic properties.

The multireference CAS+DDCI [1] and related LCAS+S [2] methods proved their high reliability and efficiency for accessing the local physics such as the magnetic exchange within experimental accuracy, however they cannot be used for systems involving more than one or two unpaired electrons per magnetic center. We will use a simple physical criterion in order to propose a new ab initio approach that overcomes this problem [3].

We used this new method to study the magneto-electric coupling in a prototypal magneto-electric system YMnO₃ [4]. Indeed we were able to computed the magnetic exchange as a function of an applied electric field within experimntal accuracy. The importance of the different microscopic contributions (piezzo-magnetic effects, spin-orbit couplign etc…) on the magneto-electric coupling will be discussed from he ab-initio results.

[1] J. Miralles, J. P. Daudey and R. Caballol, Chem. Phys. Lett. 198, (1992) 555 ; V. M. García et al., Chem. Phys. Lett. 238, (1995) 222 ; V. M. García, M. Reguero and R. Caballol, Theor. Chem. Acc. 98, (1997) 50.
[2] A. Gellé, M. L. Munzarová, M.B. Lepetit and F. Illas, Phys. Rev. B 68, 125103 (2003) ; C J. Calzado, J. F. Sanz and J. P. Malrieu, J. Chem. Phys. 112, 5158 (2002).
[3] A. Gellé, J. Varignon et M.-B. Lepetit, EPL 88 37003 (2009).
[4] J. Varignon and M.-B. Lepetit, in preparation.