Dipole Moment of Two Electrons

[zachzach]

Why is the dipole moment of two electrons equal to zero?

$$<br /> \vec{d} = \sum{q_{i}\vec{r_{i}}}<br />$$

The distance between them is nonzero and they both have charges. It is not obvious to me why this sums to zero.

 

[Meir Achuz]

If their center of mass is taken as the origin, then Sum r_i=0.