🔷 Vacancy Diffusion in a Crystal: Equilibrium Vacancies, Random-Walk Hopping and Arrhenius Activation Energy

A 1,728-site crystal with vacancies that hop by kinetic Monte Carlo: equilibrium vacancy fraction from Boltzmann statistics, tracer self-diffusion with the simple-cubic correlation factor, an Arrhenius sweep that recovers Ev + Em, and a slice view through the lattice.