Transition path sampling computing rates

The calculation of reaction rate constants with the transition path sampling methods does not require understanding of the reaction mechanism, for instance in the form of an appropriate reaction coordinate. If such information is available other methods such as the reactive flux formalism are likely to yield reaction rate constants at a lower computational cost than transition path sampling. 

In chapter 6, we study the diffusion of isobutane in Silicalite. At low pressures, isobutane is preferentially adsorbed at the intersections of Silicalite. As there is a large free energy barrier between two intersections, the jump of an isobutane molecule to a nearby intersection will be a rare event. Therefore, we cannot use conventional Molecular Dynamics (MD) to compute the jump rate (and therefore also the diffusion coefficient). To compute the diffusion coefficient, we have used transition path sampling. In these simulations, we generate an ensemble of MD tra-... 

Differential scanning calorimetry (DSC) analyzes thermal transitions occurring in polymer samples when they are cooled down or heated up under inert atmosphere. Melting and glass transition temperatures can be determined as well as the various transitions in liquid crystalline mesophases. In a typical DSC experiment, two pans are placed on a pair of identically positioned platforms connected to a furnace by a common heat flow path. One pan contains the polymer, the other one is empty (reference pan). Then the two pans are heated up at a specific rate (approx. 10 K min ). The computer guarantees that the two pans heat at exactly the same rate -despite the fact that one pan contains polymer and the other one is empty. Since the polymer sample is extra material, it will take more heat to keep the temperature of the sample pan increasing at the same rate as the reference pan. A plot is created where the difference in heat flow between the sample and reference is plotted as a function of temperature. When there is no phase transition in the polymer, the plot parallels the x-axis, and the heat flow is given in units of heat, q, supplied per unit time, t ... 

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