Hello Liu, I think one need to be careful about the parameter 'MD.MaxForceTol' in the geometry relaxation. By default it is 0.04 eV/A, and it may be too large to get a good enough relaxed structure.
Xiaoliang ----- Original Message ----- From: "liuyunlong0902" <[email protected]> To: [email protected] Sent: Sunday, October 9, 2011 12:54:45 PM GMT -05:00 US/Canada Eastern Subject: [SIESTA-L] Negative value in phonon spectrum Dear siesta users, As we konw that there should be no negative value in phonon spectrum, but when I tried to draw the phonon spectrum of bilayer-graphene, there are always some negative intervals. I'am very confused about this. My program attached. Best regards Liu _____________________________________________________________- NumberOfSpecies 1 %block chemicalspecieslabel 1 6 C %endblock chemicalspecieslabel PAO.BasisSize DZP MeshCutoff 170.0 Ry DM.MixingWeight 0.001 /0.01/0.1 DM.NumberPulay 3 DM.Tolerance 1.0d-5 %include FC.fdf NumberOfAtoms 4 LatticeConstant 2.45951215 Ang %block LatticeVectors 0.8660254 0.5 0.0 0.8660254 -0.5 0.0 0.0 0.0 8.0 %endblock LatticeVectors AtomicCoordinatesFormat NotScaledCartesianAng %block AtomicCoordinatesAndAtomicSpecies -0.000007 0.000017 -0.127708 1 12.01 1.419987 0.000012 -0.127709 1 12.01 -0.000021 -0.000010 3.725312 1 12.01 1.419990 -0.000005 3.725319 1 12.01 %endblock AtomicCoordinatesAndAtomicSpecies SuperCell_1 3 SuperCell_2 3 SuperCell_3 0 AtomicDispl 0.2 Bohr BandLinesScale pi/a %block BandLines 1 0.000 0.000 0.000 \Gamma 173 1.1547005 0.000 0.000 M 100 1.1547005 0.666666667 0.000 K 200 0.000 0.000 0.000 \Gamma %endblock BandLines
