Simulation of Dielectric Spectra
Date du début: 1 avr. 2013,
Date de fin: 31 mars 2015
"Modern spectroscopic techniques allow to measure the frequency dependent dielectric permittivity of complex liquids over about 18 decades, accessing relaxation times ranging from several hours down to the picosecond scale. The central problem in interpreting dielectric spectra is to relate the spectral features to the underlying dynamics of the molecular or atomic components of the fluids. Molecular dynamics simulations could provide in this sense invaluable help. However, a large number of important relaxation processes, responsible for spectral peaks, originate from rare events, the presence of which can severely limit the potential of this simulation technique. Up until now, only standard molecular dynamics simulations have been employed to investigate dielectric spectra, and the capabilities of enhanced sampling techniques such as metadynamics or parallel tempering have been largely neglected in this field. In addition, liquids other than water have received relatively little attention in the framework of computational dielectric spectroscopy, even though plenty of important problems are still waiting for an answer. I will fill this gap by putting forward an approach which combines the knowledge of the free energy landscape provided by enhanced sampling techniques with the information accessible by molecular dynamics simulations. I will use this novel approach to tackle two compelling problems (the origin of the excess wing in liquid glycerol spectra and the ion pairing properties in room temperature ionic liquids) in the fundamental understanding of two materials which are crucial for the modern economy. The SIDIS approach is expected to have an important impact on the field of computational dielectric spectroscopy, as it will lay the foundations of a new data analysis paradigm that allows to perform assignments of spectral features never done before, therefore providing a major contribution to the advancement of this field."
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