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,

${\displaystyle \epsilon =\epsilon _{\infty }+{\frac {4\pi (\langle M^{2}\rangle -\langle M\rangle ^{2})}{3\langle V\rangle k_{B}T}}}$

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