[Pw_forum] imaginary frequency at extended Q point

潭影空人心 774729155 at qq.com
Tue Oct 20 03:36:53 CEST 2015


Dear all,   I used nq1 = 2, nq2 = 2, nq3 = 2 and nq1 = 4, nq2 = 4, nq3 = 4 ,respectively, to do a phonon calculation. There is no imaginary frequency at the calculated Q points, but after calculations of Q2R and MATDYN, imaginary frequencies appear near GAMMA point(not GAMMA point).


My settings are as follows:
1.lattice relaxation under pressure:
&control                                                          
    calculation               = 'vc-relax'                                          
    restart_mode              = 'from_scratch'
    prefix                    = 'cras'                                                  
    pseudo_dir                = '/data1/tan1/software/espresso-5.1/pseudo/'
    outdir                    = './tempdir/' 
    etot_conv_thr             = 1.0D-6
    forc_conv_thr             = 1.0D-4
    tstress                   = .true.
    tprnfor                   = .true.                                                
/                                                                        
&system                                                                  
    ibrav                     = 8
    A                         = 5.58
    B                         = 3.36
    C                         = 6.17
    nat                       = 8
    ntyp                      = 4
    ecutwfc                   = 120
    occupations               = 'smearing'
    smearing                  = 'methfessel-paxton'
    degauss                   = 0.04
    nspin                     = 2
    starting_magnetization(1) = -1
    starting_magnetization(2) = 1
    starting_magnetization(3) = 0 
    starting_magnetization(4) = 0
/                                                                  
&electrons                                                        
    electron_maxstep          = 100
    conv_thr                  = 1.0d-6
    mixing_beta               = 0.7                                              
/        
&ions                                             
    ion_dynamics             = 'bfgs'         
/                                                       
&cell                      
   press                     = 1500
   cell_dynamics             = 'bfgs' 
   press_conv_thr            = 0.1      
   cell_factor               = 2.5d0
/
ATOMIC_SPECIES                                                     
   Cr1   51.9961       Cr.pz-hgh.UPF
   Cr2   51.9961       Cr.pz-hgh.UPF
   As1   74.9216       As.pz-hgh.UPF
   As2   74.9216       As.pz-hgh.UPF
ATOMIC_POSITIONS (crystal)                                            
Cr1   0.012000      0.250000      0.201000  1 0 1
Cr2   0.988000      0.750000      0.799000  1 0 1
Cr2   0.512000      0.250000      0.299000  1 0 1
Cr1   0.488000      0.750000      0.701000  1 0 1
As1   0.195000      0.250000      0.582000  1 0 1
As2   0.805000      0.750000      0.418000  1 0 1
As2   0.695000      0.250000      0.918000  1 0 1
As1   0.305000      0.750000      0.082000  1 0 1
K_POINTS {automatic}                                                                   
6 8 6 0 0 0                         





2.interior coordination relaxation:
All is the same as above, but "ecutwfc = 50"
3.self-consistent iteration for phonon calculation:
&control                                                               calculation               = 'scf'                                               restart_mode              = 'from_scratch'     prefix                    = 'cras'                                                       pseudo_dir                = '/data1/tan1/software/espresso-5.1/pseudo/'     outdir                    = './tempdir/'      tstress                   = .true.     tprnfor                   = .true.                                                 /                                                                         &system                                                                       ibrav                     = 0     celldm(1)                 = 10.54467182     nat                       = 8     ntyp                      = 4     ecutwfc                   = 50     occupations               = 'smearing'     smearing                  = 'methfessel-paxton'     degauss                   = 0.05     nspin                     = 2     starting_magnetization(1) = -1     starting_magnetization(2) = 1     starting_magnetization(3) = 0     starting_magnetization(4) = 0 /                                                                   &electrons                                                             electron_maxstep          = 200     conv_thr                  = 1.0d-10     mixing_beta               = 0.7                                               /         ATOMIC_SPECIES                                                         Cr1   51.9961       Cr.pz-hgh.UPF    Cr2   51.9961       Cr.pz-hgh.UPF    As1   74.9216       As.pz-hgh.UPF    As2   74.9216       As.pz-hgh.UPF CELL_PARAMETERS (alat= 10.54467182)               0.9146 0.0000 0.0000 0.0000 0.4765 0.0000 0.0000 0.0000 0.9628   ATOMIC_POSITIONS (crystal)                        Cr1 0.0104 0.2500 0.1827  Cr2 0.9896 0.7500 0.8173  Cr2 0.5104 0.2500 0.3173  Cr1 0.4896 0.7500 0.6827  As1 0.1833 0.2500 0.5616  As2 0.8167 0.7500 0.4384  As2 0.6833 0.2500 0.9384  As1 0.3167 0.7500 0.0616  K_POINTS {automatic}                                                                    6 8 6 0 0 0                          
4.self-consistent iteration for electron-phonon coupling:
All is the same as phonon calculation but k-mesh 12 16 12,and in addition to "la2F = .true.".
5.phonon calculation:
&inputph   tr2_ph       = 1.0d-11   prefix       = 'cras'   fildvscf     = 'crasdv'   amass(1)     = 51.9961   amass(2)     = 51.9961   amass(3)     = 74.9216   amass(4)     = 74.9216   outdir       = './tempdir/',   fildyn       = 'cras.dyn',   electron_phonon='interpolated'   el_ph_sigma  = 0.005,   el_ph_nsigma = 10,   trans        = .true.   ldisp        = .true.   alpha_mix(1) = 0.5   recover      =.true.   nq1          = 2   nq2          = 2   nq3          = 2  /
6.q2r:
 &input   zasr='crystal',  fildyn='cras.dyn', flfrc='cras222.fc',   la2F=.true.  /
7.&input     asr='crystal', amass(1)=51.9961,amass(2)=51.9961,amass(3)=74.9216,amass(4)=74.9216,      flfrc='cras222.fc', flfrq='cras.freq', q_in_band_form=.true.,     la2F=.true.,dos=.false.  / 8 0.000000 	0.000000 	0.000000 	50 0.500000 	0.000000 	0.000000 	50 0.500000 	0.785906 	0.000000 	50 0.000000 	0.000000 	0.000000 	50 0.000000 	0.000000 	0.456275 	50 0.500000 	0.000000 	0.456275 	50 0.500000 	0.785906 	0.456275 	50 0.000000 	0.000000 	0.456275 	1



I am eagerly hoping someone can help me. Thank you.
tanlin2015.10.20
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