Dipole

[classi] [classj] dipole [sigma_0] [mu]

$$U_{\mathrm{dipole}} = \frac{\mu^2 \sigma_0^3}{r^3} \left[ \hat{\m... ...t(\hat{\mu}_i \cdot \hat{r}\right)\left(\hat{\mu}_j \cdot \hat{r}\right)\right]$$ (6)

where $\mu$ is the dipole strength, $\hat{\mu}_i$ is the dipole orientation of the $i$-th site, $r$ is the distance between sites $i$ and $j$, and $\hat{r}$ is the unit vector pointing between the sites.