Danny Perez Los Alamos National Laboratory Theoretical Division T-1 When describing kinetics in the solid state, (e.g., of nucleation, diffusion, or reaction of defects) the role of the energetic component of the activation free energy barrier is usually emphasized, while the vibrational entropic contributions are often assumed to behave in a “standard” way. While this rule of thumb is mostly adequate, it can sometimes fail dramatically. In this talk, I will present a scalable method to directly and efficiently compute vibrational prefactors in the context of Harmonic Transition State Theory. This method is based on a Kernel Polynomial Method approximation to the vibrational density of states. I will then discuss an example of the breakdown of the standard picture of energy-dominated barriers in the case of heterogeneous nucleation of dislocations at preexisting nanoscale voids in materials under tension. In certain regimes, this system is purely stabilized by entropic contributions, which leads to very unusual nucleation kinetics.