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Hi <span>Stefano and others</span>, </p>
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Thank you for your helpful response! </p>
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<p style=""><span style="font-size: 12pt;">We are fairly new to both QE and phonon calculations, and have been trying to simulate the Raman spectrum of an extended 2D sheet using the primitive cell and also a 3x3 supercell. A phonon </span><span style="font-size: 12pt;">calculation
at q=0 </span><span style="font-size: 12pt;">of the primitive cell produces results that are very close to experiment (at 16x16x1 Monkhorst pack k-points, 1e-8 Ry for electronic convergence, and a kinetic energy cutoff of 50 Ry). However, calculation of the
3x3 supercell at q=0 </span><span style="color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, Helvetica, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">(using
the same convergence criteria and 8x8x1 k-points)</span><span style="font-size: 12pt;"> produces additional Raman active modes, as well as shifting some of the modes present in the primitive cell to different energies. If the additional Raman active modes
in the supercell are from q/=0 in the primitive cell, why might these be Raman active? Also, is it
</span>possible<span style="font-size: 12pt;"> to reliably simulate the Raman spectrum of a 3x3 or larger supercell?</span></p>
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<span style="font-size: 12pt;">Thank you again for your help with this.</span><br>
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px"><span style="color:rgb(34,34,34); font-family:arial,sans-serif; font-size:12.8px">-- </span><br>
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px"><span style="color:rgb(34,34,34); font-size:9pt; font-family:"Times New Roman",serif">Charlie Ruffman | <span style="color:rgb(31,78,121)">BSc<br>
</span></span><span style="color:rgb(31,78,121); font-family:"Times New Roman",serif; font-size:12px">BSc(Hons) </span><span style="color:rgb(34,34,34); font-size:9pt; font-family:"Times New Roman",serif"><span style="color:rgb(31,78,121)">Student<br>
</span><br>
<span style="color:rgb(31,78,121)">Chemistry Department<br>
University of Otago</span> <span style="color:rgb(59,56,56)"><br>
</span><span style="color:rgb(31,78,121)">Tel</span> 64 3 479 7930<br>
<span style="color:rgb(31,78,121)">PO Box 56, Dunedin 9054</span><br>
<span style="color:rgb(31,78,121)">New Zealand</span> <br>
<br>
<span style="color:rgb(31,78,121)">Website</span> </span><font color="#0000ff" face="Times New Roman, serif" style="font-size:12.8px"><span style="font-size:12px"><u><a href="http://neon.otago.ac.nz/research/alg/" target="_blank" id="LPNoLP" style="color:rgb(17,85,204)">http://neon.otago.ac.<wbr>nz/research/alg/</a></u></span></font></div>
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