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Speakers: Ivan Štich (Institute of Physics, Slovak Academy of Sciences, Bratislava)
Place: Institute of informatics and automation, Pod vodárenskou věží 1143/4, ground floor, room no. 25
Presented in English
Organisers:
Department of Condensed Matter Theory
Abstract:
Ultra-accurate Quantum Monte-Carlo (QMC) methods for fermions
ideally combine accuracy of the best quantum chemistry methods with
favorable asymptotic scaling with system size typical for mean-field methods.
In the first part an elementary introduction into the main challenges of
the QMC methods (nodal hypersurfaces, consistent optimization of electronic
and atomic structure, QMC dynamics, etc.) will be given. In the second
part application of the QMC method to systems currently studied, pi-bonded
azobenzene (AB) and organometallic vanadiumbenzene (VBz) molecules, will
be discussed. These systems not only represent completely different limits
of chemical bonding but they also find radically different practical
applications. AB is a photoswitchable molecule with applications in
opto-electronic nano-devices and sensors, while
organometallic systems with transition metal atoms are spintronic
materials. In AB we have described the ground-state (S0) and a few excited
singlet (S1, S2), and triplet (T1, T2,.) states with ultra high accuracy
of 0.1 eV. Such accuracy not only yields excellent agreement with experiments
but is sufficient to disentangle the strongly overlapping singlet and triplet
states in the experimental EEL (electron energy loss) spectra. Despite
application of VBz as spin valves, experimental and theoretical knowledge
of electronic structure (spin multiplicity, dissociation, ionization energies,
etc.) is limited. QMC simulations indicate electronic structure distinctly
different from that predicted by density functional theory. At the same time
the QMC results reveal also possible experimental biases.
* Work done in collaboration with M. Dubecký, R. Derian (Institute of
Physics SAS) and L. Mitas (North Carolina State University)
Copyright © 2008-2010, Fyzikální ústav AV ČR, v. v. i.
