Christian Schroder (Université de Vienne, Autriche) présentera jeudi 6 juillet à 14h, barre 43/44, salle 317 :, un séminaire intitulé :
Computational spectroscopy of (polarizable) ionic liquids
Abstract
Ionic liquids form a class of complex liquids as they consist of charged, dipolar species. The delocalization and the flexibility of the electron density are the origin of the amphiphilic character of ionic liquids and make them promising alternatives to conventional, volatile solvents in many applications.
However, ionic liquids are also interesting from a theoretical point of view. Since classical molecular dynamics force fields are not able to reproduce the dynamics, polarizable forces on the basis of induced dipoles are essential.
This way, the flexibility of the partial charge distribution and the resulting effective screening of Coulomb forces can be reproduced to accelerate the overall dynamics while keeping hydrogen bonds intact.
In contrast to quantum-chemical calculations, polarizable molecular dynamics simulations are also capable to follow the dynamics of thousands of ion pairs over several dozens or even hundreds of nanoseconds [1]. Both, these system sizes and simulation periods are a must for evaluating computational spectra : Starting in the MHz frequency regime, ion pair dynamics can be studied by the nuclear Overhauser effect [2,3]. Dielectric spectroscopy measures the rotational and translational response of single ions as well as polar and apolar domains to an external field from the MHz to the THz frequency regime [4, 5]. Solvation dynamics in the THz regime can also be studied by a local electric field emerging from the laser excitation of a chromophore [2].
However, dielectric spectra and the resulting Stokes shift relaxation are related to each other [6].
References
[1] S. Gabl, C. Schroder, and O. Steinhauser. “Computational studies of ionic liquids : Size does matter and time too.” J. Chem. Phys., 137(2012), 094501.
[2] M. Schmollngruber, C. Schroder, and O. Steinhauser. “Polarization effects on the solvation dynamics of
coumarin C153 in ionic liquids : Components and their cross-correlations.” J. Chem. Phys., 138(2013), 204504.
[3] S. Gabl, C. Schroder, D. Braun, H. Weingartner, and O. Steinhauser. “Pair dynamics and the intermolecular nuclear overhauser effect (noe) in liquids analysed by simulation and model theories : Application to an ionic liquid.” J. Chem. Phys., 140(2014), 184503.
[4] C. Schroder and O. Steinhauser. “On the dielectric conductivity of molecular ionic liquids.” J. Chem. Phys., 131(2009), 114504.
[5] C. Schroder, T. Sonnleitner, R. Buchner, and O. Steinhauser. “The influence of polarizabilty on the dielectric spectrum of the ionic liquid 1-ethyl-3-methylimidazolium triflate.” Phys. Chem. Chem. Phys., 13(2011), 12240.
[6] M. Schmollngruber, C. Schroder, and O. Steinhauser. “Dielectric spectra of ionic liquids and their conversion to solvation dynamics : a detailed computational analysis of polarizable systems.” Phys. Chem. Chem. Phys., 16(2014), 10999.
