  Grain boundary (GB) properties greatly influence the mechanical, electrical,
and thermal response of polycrystalline materials. Most computational studies
of GB properties at finite temperatures use molecular dynamics (MD), which is
computationally expensive, limited in the range of accessible timescales, and
requires cumbersome techniques like thermodynamic integration to estimate free
energies. This restricts the reasonable computation (without incurring
excessive computational expense) of GB properties to regimes that are often
unrealistic, such as zero temperature or extremely high strain rates.
Consequently, there is a need for simulation methodology that avoids the
timescale limitations of MD, while providing reliable estimates of GB
properties. The Gaussian Phase-Packet (GPP) method is a temporal
coarse-graining technique that can predict relaxed atomic structures at finite
temperature in the quasistatic limit. This work applies GPP, combined with the
quasiharmonic approximation for computing the free energy, to the problem of
determining the free energy and shear coupling factor of grain boundaries in
metals over a range of realistic temperatures. Validation is achieved by
comparison to thermodynamic integration, which confirms that the presented
approach captures relaxed-energy GB structures and shear coupling factors at
finite temperature with a high degree of accuracy.
