Energy and heat transport in molecules
AuthorPandey, Hari Datt
AdvisorLeitner, David M
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We investigate the effect of thermalization and boundary conductance of the various molecular junctions using the Fermi's golden rule type of theoretical, computational arrangements. The studied systems have a wide range of advanced technological application. The quantification of the energy rectification and origin of the energy diode characteristics were estimated for the small organic molecules, alkylbenzenes, in the liquid phase. Boundary conductance and its common properties were calculated for the three different types of molecular junction and interfaces. The molecular junction we have studied here are water-sugar-gold nanoparticle (GNP), metal-alkane chain-sapphire, metal-fluorinated alkane-Sapphire and water-polyethylene glycol (PEG)-GN. We also estimated the underlying Fermi resonances and energy flow pathway for the azide and nitrile vibrational probes.Ultrafast IR pump Raman probe [J. Phys. Chem. B 117, 10898 (2013) and J. Phys. Chem. A, 2014, 118 (6), pp 965–973] reveal the asymmetric vibrational energy flow across some substituted benzenes. Here we explore theoretically energy flow in toluene and liquid alkylbenzenes that were probed in the experiments and show that quantum mechanical bottlenecks to the relaxation in the initially excited states, which is basically the scarcity of local density of coupled states, and the competition between the relaxation time are the primary reasons for the rectification. We have calculated the thermalization rate using the golden rule type formalism, and boundary conductance using the Landauer formalism along with inelastic and elastic scattering rates for the junctions. We found that the Landauer formalism can estimates well enough the boundary conductance across the molecular junctions if the inelastic scattering due to the anharmonic interactions have a negligible impact on the boundary conductance across the junctions. The calculated boundary conductance well agrees with the experiments for all of the systems we have computed.