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<p>Greetings,</p>
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<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3"><font face="Calibri">I am trying to understand a detail of the D3
</font></font><font size="3"><font face="Calibri">suite. Some literature suggests that it can be used to calculate the decay
</font></font><font size="3"><font face="Calibri">of phonons at any q-point. Looking at the code and at the inpt required by d3.x though, my first interpretation is that it</font></font><font size="3"><font face="Calibri"> works for Gamma phonon decaying through
a q,-q channel. </font></font></p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3" face="Calibri"></font> </p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3"><font face="Calibri">In the calculation of force constant derivatives, the d3.x program requires</font></font></p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3"><font face="Calibri">the perturbed densities at q0=0 and at the q of the decay channel,</font></font><font size="3"><font face="Calibri"> producing V^(3)(0,q,-q) .
</font></font></p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3"><font face="Calibri">T</font></font><font size="3"><font face="Calibri">o calculate V^(3)(k,q,k-q), does it make any sense to input </font></font><font size="3"><font face="Calibri">fildrho
given by a calculation at q, and<span> </span>fild0rho given by a </font></font><font size="3"><font face="Calibri">calculation at k? The calculation seems to work but I am not sure whether it is meaningful, i.e., whether this can be used to calculate the
decay of a k-point phonon through q and a k-q phonons.</font></font></p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3" face="Calibri"></font> </p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3" face="Calibri">Thank you for any hint.</font></p>
<p style="MARGIN: 0in 0in 0pt" class="MsoPlainText"><font size="3" face="Calibri">--Stefan</font></p>
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