Molecular Simulation/Dielectric constants

The dielectric constant of a liquid can be calculated from the magnitude of the variance in the net dipole moment of a cubic simulation cell, M,
 * $$\epsilon = \epsilon_{\infty} + \frac {4\pi (\langle M^{2} \rangle-\langle M \rangle ^{2})}{3 \langle V \rangle k_{B}T}$$

where V is the volume of the simulation cell. $$\epsilon_{\infty}$$ is the infinite frequency dielectric constant. For non-polarizable models, this term is equal to 1.