_zf(Sys,eSpins,'sparse')
</pre>

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<div class="subtitle">Description</div>

<p>
This function computes the <a href="hamiltonian.html#zfi">Hamiltonian</a> of all electronic zero-field
interactions (ZFIs) in the <a href="spinsystem.html#D">spin system</a> described by the structure
<code>Sys</code>.
</p>

<p>
If the vector <code>eSpins</code> is given, the ZFI of only the specified electron spins is returned (1 is the first electron spin, 2 the
sec