[Pw_forum] imaginary frequency at extended Q point
Lorenzo Paulatto
lorenzo.paulatto at impmc.upmc.fr
Tue Oct 20 09:19:43 CEST 2015
Dear 潭影空人心,
the imaginary frequencies could just be an artifact of the Fourier
interpolation procedure, which means that you need to do the ph.x calculation
on a finer grid.. If that is not possible, your best bet is to try to push
convergence a bit and try to change the method of acoustic sum rule used.
hth
On Tuesday, October 20, 2015 09:36:53 AM 潭影空人心 wrote:
> 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
--
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
+33 (0)1 44 275 084 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/
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