.. _ug_tb_sh_4-1:

************
(4, 1) terms
************

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

.. math::
    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}


Relevant API
============

*   :py:attr:`magnopy.Convention.c41`

    Convention constant.

*   :py:meth:`magnopy.SpinHamiltonian.add`

    Method to add the parameter to the Hamiltonian.

*   :py:meth:`magnopy.SpinHamiltonian.remove`

    Method to remove the parameter from the Hamiltonian.

*   :py:attr:`magnopy.SpinHamiltonian.p41`

    An iterator over the parameters already added to the Hamiltonian.