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<FONT color=#000000>Dear users:</FONT><BR>
<FONT color=#000000></FONT> <BR>
<FONT color=#000000> I have calculated the phonon dispersion of zinc-blende CrSb. Before calculating phonon dispersion, I relaxed the CrSb lattice and got the optimized lattice parameters,which agreed well with that in previous literature, and after ph.x calculation I found that the two lower frequences at X(-1.0 0.0 0.0) are imaginary,which indicates the lattice instability of two modes.The frequencies are shown as following</FONT><BR>
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<FONT color=#000000> q = -1.0000 0.0000 0.0000<BR> **************************************************************************<BR> omega( 1) = -2.790113 [THz] = -93.068763 [cm-1]<BR> ( 0.000000 0.000000 -0.403189 0.000000 0.754599 0.000000 )<BR> ( 0.000000 0.000000 0.456614 0.000000 -0.243973 0.000000 )<BR> omega( 2) = -2.790113 [THz] = -93.068763 [cm-1] <BR> ( 0.000000 0.000000 -0.754599 0.000000 -0.403189 0.000000 )<BR> ( 0.000000 0.000000 -0.243973 0.000000 -0.456614 0.000000 )<BR> omega( 3) = 3.418041 [THz] = 114.014317 [cm-1] <BR> ( 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )<BR> ( -1.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )<BR> omega( 4) = 3.580039 [THz] = 119.418057 [cm-1]<BR> ( 1.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )<BR> ( 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )<BR> omega( 5) = 5.338839 [THz] = 178.085673 [cm-1]<BR> ( 0.000000 0.000000 -0.817099 0.000000 0.000000 0.000000 )<BR> ( 0.000000 0.000000 0.000000 0.000000 0.576498 0.000000 )<BR> omega( 6) = 5.338839 [THz] = 178.085673 [cm-1]<BR> ( 0.000000 0.000000 0.000000 0.000000 -0.817099 0.000000 )<BR> ( 0.000000 0.000000 0.576498 0.000000 0.000000 0.000000 )<BR> **************************************************************************</FONT><BR>
<FONT color=#000000></FONT> <BR>
<FONT color=#000000>Usuallly, <FONT color=#ff0000>an instability implys that the atoms are not located in local minimum energy postion</FONT>,thus next I displaced atoms in the cell accroding to the eigen-displacements shown above,and got a cubic cell containg 8 atoms. </FONT><FONT color=#ff0000>But I found the energy rised with the increase of atom displacements, which was totally contrary to what I expected. In fact, only the decrease of energy with atom displacments will be consistent the results from phonon self-consitsten calculation.</FONT><BR>
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<FONT color=#000000>The electronic structure calculation input file and phonon input file are list as : </FONT><BR>
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<FONT color=#000000></FONT> <BR>
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<FONT color=#000000>### electronic structure calculation </FONT><BR>
<FONT color=#000000>####</FONT><BR>
<FONT color=#000000> &CONTROL<BR> title = CrSb ,<BR> calculation = 'scf' ,<BR> restart_mode = 'from_scratch' ,<BR> prefix='CrSb',<BR> pseudo_dir = '/home/phymwm/PWSCF/espresso-3.2.3/pseudo' ,<BR> /<BR> &SYSTEM<BR> ibrav = 2,<BR> celldm(1) = 11.55,<BR> nat = 2,<BR> ntyp = 2,<BR> ecutwfc=60,<BR> ecutrho=600,<BR> occupations = 'smearing' ,<BR> degauss = 0.025 ,<BR> smearing = 'methfessel-paxton' ,<BR> nspin = 2 ,<BR> starting_magnetization(1) = 3.0,<BR> starting_magnetization(2) = 1.0,<BR> /<BR> &ELECTRONS<BR> electron_maxstep = 200,<BR> conv_thr = 1.0D-8 ,<BR> /<BR>ATOMIC_SPECIES<BR> Cr 52.00000 Cr.pw91-sp-van.UPF<BR> Sb 121.80000 Sb.pw91-n-van.UPF<BR>ATOMIC_POSITIONS alat<BR> Cr 0.000000000 0.000000000 0.000000000<BR> Sb 0.250000000 0.250000000 0.250000000<BR>K_POINTS automatic<BR> 8 8 8 0 0 0<BR> </FONT><BR>
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<FONT color=#000000>#####</FONT><BR>
<FONT color=#000000>###</FONT><BR>
phonon dispersion for CrSb<BR> &inputph<BR> tr2_ph=1.0d-16,<BR> prefix='CrSb',<BR> fildvscf='dv',<BR> amass(1)=52.00,<BR> amass(2)=121.8,<BR> outdir='./',<BR> fildyn='CrSb.dyn',<BR> trans=.true.,<BR> ldisp=.true.<BR> nq1=4, nq2=4, nq3=4<BR> /<BR>
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Thanks in advance !<BR>
<BR>
Wenmei Ming <BR>
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