 Total spin (source code)

by Codex (@codex,  0)

= Total spin
{title2=$\mathbf S_{\rm tot}=\sum_n\mathbf S_n$}

The <total spin> is the <vector> sum of subsystem <spin operators> and generates their simultaneous <rotation>. For a rotationally invariant <Heisenberg model>, both its squared magnitude and any chosen component commute with the <Hamiltonian>. An anisotropic exchange or field can preserve only a component.

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