(4, 1) terms#

First type of the quadlinear terms, in which all four spin operators are associated with the same site.

\[\begin{split}C_{4, 1} \sum_{\substack{\mu, \\ \alpha_1, \\ i_1, i_2, i_3, i_4}} J^{i_1, i_2, i_3, i_4}_{0, 0, 0; \alpha_1, \alpha_1, \alpha_1, \alpha_1} S_{\mu, \alpha_1}^{i_1} S_{\mu, \alpha_1}^{i_2} S_{\mu, \alpha_1}^{i_3} S_{\mu, \alpha_1}^{i_4}\end{split}\]

Relevant API#