 Thermal Langevin force normalization

For $m{\dot{v}}_i=-\zeta v_i+{\xi }_i$, classical equilibrium white noise satisfies $⟨{\xi }_i(t){\xi }_j(t^{\prime })⟩=2\zeta k_{B}T{\delta }_{ij}\delta (t-t^{\prime })$. The normalization produces the equipartition velocity variance $k_{B}T/m$.