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Dear all,<div><br></div><div>I am calculating the phonon modes at Gamma=0 for a 42 Carbon atom supercell. If N=42 then one has 3N= 3*42 modes= 128 modes. Just to confirm:</div><div><br></div><div>(1) Are all the modes vibrational?</div><div><br></div><div>(2) Are any modes missing from the calculation like optical or accoustical modes?</div><div><br></div><div>(3) i did the calculation and got two of the modes negative which means either threshold is high or the ecutwav must be at least eight times ecutrho. Is a threshold of 10^(-15) still too high for such a system?</div><div><b><br></b></div><div><b><br></b></div><div>Thanks</div><div><br></div><div>Elie</div><div>University of Nottingham</div><div>NG7 2RD</div><div>UK</div> </div></body>
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