Deviations from Debye's specific heat due to excess energy fluctuations (opens in new tab)

Measured specific heats often exceed Debye's T^3-law, even in high-purity single crystals. Analogous excess energy fluctuations in molecular dynamics (MD) simulations of crystals with no defects come from fast energy modulations involving next-nearest-neighbor atoms. Here, a theory is developed for these modulations, based on time- and phase-averaging followed by thermal averaging. This order of averaging is guided by evidence from the simulatio...