Dear users:
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
q = -1.0000 0.0000 0.0000
**************************************************************************
omega( 1) = -2.790113 [THz] = -93.068763 [cm-1] ( 0.000000 0.000000
-0.403189 0.000000 0.754599 0.000000 ) ( 0.000000 0.000000
0.456614 0.000000 -0.243973 0.000000 ) omega( 2) = -2.790113
[THz] = -93.068763 [cm-1] ( 0.000000 0.000000 -0.754599 0.000000
-0.403189 0.000000 ) ( 0.000000 0.000000 -0.243973 0.000000
-0.456614 0.000000 ) omega( 3) = 3.418041 [THz] = 114.014317
[cm-1] ( 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
) ( -1.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )
omega( 4) = 3.580039 [THz] = 119.418057 [cm-1] ( 1.000000
0.000000 0.000000 0.000000 0.000000 0.000000 ) ( 0.000000
0.000000 0.000000 0.000000 0.000000 0.000000 ) omega( 5) =
5.338839 [THz] = 178.085673 [cm-1] ( 0.000000 0.000000 -0.817099
0.000000 0.000000 0.000000 ) ( 0.000000 0.000000 0.000000
0.000000 0.576498 0.000000 ) omega( 6) = 5.338839 [THz] =
178.085673 [cm-1] ( 0.000000 0.000000 0.000000 0.000000 -0.817099
0.000000 ) ( 0.000000 0.000000 0.576498 0.000000 0.000000
0.000000 )
**************************************************************************
Usuallly, an instability implys that the atoms are not located in local
minimum energy postion,thus next I displaced atoms in the cell accroding to the
eigen-displacements shown above,and got a cubic cell containg 8 atoms. 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.
The electronic structure calculation input file and phonon input file are list
as :
### electronic structure calculation
####
&CONTROL title = CrSb , calculation =
'scf' , restart_mode = 'from_scratch' ,
prefix='CrSb', pseudo_dir =
'/home/phymwm/PWSCF/espresso-3.2.3/pseudo' , / &SYSTEM
ibrav = 2, celldm(1) = 11.55, nat =
2, ntyp = 2, ecutwfc=60,
ecutrho=600, occupations = 'smearing' ,
degauss = 0.025 , smearing = 'methfessel-paxton' ,
nspin = 2 , starting_magnetization(1) = 3.0,
starting_magnetization(2) = 1.0, / &ELECTRONS electron_maxstep =
200, conv_thr = 1.0D-8 , /ATOMIC_SPECIES Cr 52.00000
Cr.pw91-sp-van.UPF Sb 121.80000 Sb.pw91-n-van.UPFATOMIC_POSITIONS alat Cr
0.000000000 0.000000000 0.000000000 Sb 0.250000000
0.250000000 0.250000000K_POINTS automatic 8 8 8 0 0 0
#####
###
phonon dispersion for CrSb &inputph tr2_ph=1.0d-16, prefix='CrSb',
fildvscf='dv', amass(1)=52.00, amass(2)=121.8, outdir='./',
fildyn='CrSb.dyn', trans=.true., ldisp=.true. nq1=4, nq2=4, nq3=4 /
Thanks in advance !
Wenmei Ming
_________________________________________________________________
MSN ????????????????????
http://cn.msn.com
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