This manual gives you a walk-through on how to use the Dipole Moment Calculation Plugin:
Dipole moment ( μ ) is the measure of net molecular polarity, and describes the charge separation in a molecule, where electron density is shared unequally between atoms. Dipole Moment Calculation Plugin calculates the total dipole moment of a molecule as a vector expressed in the principal axis frame. The dipole moment is calculated from the molecular geometry and the atomic partial charges. Its unit is Debye (D).