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<div><span>Many thanks.</span></div><div><span>I will refresh the textbooks.</span></div><div><span><br></span></div><div><span>Best,</span></div><div><span>Yi Wang</span></div>
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<div style="font-size:12px;line-height:1.5;word-break:break-all;margin-left:10px;margin-right:10px">On <span class="mail-date">5/10/2018 19:44</span>，<a class="mail-to" style="text-decoration:none;color:#2a83f2;" href="mailto:paulatz@gmail.com">Lorenzo Paulatto<paulatz@gmail.com></a> wrote： </div>
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<div dir="auto"><div data-smartmail="gmail_signature" dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:"\005fae\008f6f\0096c5\009ed1";line-height:1.6"><div><div><span style="line-height:22.4px">Yes, I understand the cost of phonon is the critical part.</span></div><div><span style="line-height:22.4px">For clarification, I meant if I perform phonon calculation on less q points (not on full gamma centered MP grids), </span></div></div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">This is not how force constants work: as they are the (discrete) Fourier transform of the dynamical matrix, they can only be computed accurately for points which are reciprocal to the q-points in the grid. </div><div dir="auto"><br></div><div dir="auto">Using shifted grids is a good trick when computing "square modulus" integrals, where the phase does not count. But the calculation of force constants is all about the phase, and shifted grids do not work very well for this case. </div><div dir="auto"><br></div><div dir="auto">The fact that you eventually want the DOS is a red herring, it is completely irrelevant to the problem.</div><div dir="auto"><br></div><div dir="auto">Kind regards </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:"\005fae\008f6f\0096c5\009ed1";line-height:1.6"><div><div><span style="line-height:22.4px">how could I get reliable real space force constants toward the calculation of DOS.</span></div><div><span style="line-height:22.4px"><br></span></div>
<div><span>Yi Wang</span></div>
<div><span style="line-height:22.4px">Nanjing University of Sci. & Tech.</span></div>
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<div style="font-size:12px;line-height:1.5;word-break:break-all;margin-left:10px;margin-right:10px">On <span class="m_6004500689821854513mail-date">5/10/2018 12:42</span>，<a class="m_6004500689821854513mail-to" style="text-decoration:none;color:#2a83f2" href="mailto:paulatz@gmail.com" target="_blank" rel="noreferrer">Lorenzo Paulatto<paulatz@gmail.com></a> wrote： </div>
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<div dir="auto">Hello, <div dir="auto">the cost of computing the phonon dos with matdyn is zero, compared to the cost of the phonon calculation itself. <br><br><div data-smartmail="gmail_signature" dir="auto">-- <br>Lorenzo Paulatto<br>Written on a virtual keyboard with real fingers</div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 10 May 2018 06:31, "Yi Wang" <<a href="mailto:wangwy13@gmail.com" target="_blank" rel="noreferrer">wangwy13@gmail.com</a>> wrote:<br type="attribution"><blockquote class="m_6004500689821854513quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div>Dear everyone,</div><div><br></div><div>As I understand, the q2r.x works only on gamma centered q grids for the DFPT calculations. However, is there any tool to calculate the real space force constant for the shift q points calculations and the manually q grid calculations?</div><div><br></div><div>If it is possible, I want to test the phonon DOS calculation on some smaller q grids for the sake of saving cost.</div><div><br></div><div>Thank for your guidance.</div><div class="m_6004500689821854513signature-text">
<div><span><br></span></div><div><span>Yi Wang</span></div><div>Nanjing University of Sci. & Tech.</div>
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