(2, 2) terms#

Second type of the bilinear terms, in which spin operators are associated with different sites. In other words, for these terms \(\boldsymbol{r}_{\mu,\alpha_1} \neq \boldsymbol{r}_{\mu + \nu_2, \alpha_2}\).

\[\begin{split}C_{2, 2} \sum_{\substack{\mu, \nu_2, \\ \alpha_1, \alpha_2, \\ i_1, i_2}} J^{i_1, i_2}_{\nu_2; \alpha_1, \alpha_2} S_{\mu, \alpha_1}^{i_1} S_{\mu + \nu_2, \alpha_2}^{i_2}\end{split}\]

Relevant API#