A component of the <tt>DVIRIAL</tt> (rank 4) tensor.

<p>
<tt>DVIRIAL_ijkl </tt> = d(<tt>VIRIAL_ij</tt>) / (d<tt>e_kl</tt>)

<p>
<tt>VIRIAL</tt> is the Virial stress tensor and <tt>e</tt> is the strain tensor.
