[QE-users] Large difference between lattice structure simulated by pwscf code and cp.x code

Stefano de Gironcoli degironc at sissa.it
Thu Apr 5 08:22:48 CEST 2018


Dear Jie Peng,

    the cp.x code assumes gamma point sampling and does not process your 
k-point definition card, while pw.x is using, a rather dense, grid of 
points in the BZ.

   I think this is the most relevant difference in your two inputs.

   To see if this is the case you can repeat the pw.x calculation with

K_POINT Gamma

   Is the 10 8 8 grid really necessary ? is the system metallic ?

   if not I guess a smaller grid (like  6 4 4 or less) could be 
sufficient and then you could use the cp.x code with a corresponding 
supercell  if you wish so.

stefano


On 05/04/2018 04:16, Jie Peng wrote:
> Dear all Quantum Espresso users:
>
> I have used pw.x and cp.x code to compute equilibrium lattice 
> structure of 1T-HfS2 (Halfnium Disulfide) respectively, and I find 
> that they give very different results.
>
> *For pwscf simulation, the input file are given below.*
> /&control/
> /    calculation='vc-relax',/
> /!    restart_mode='from_scratch',/
> /    tstress = .true./
> /    tprnfor = .true./
> //
> /    wf_collect=.true./
> /    etot_conv_thr=1e-6/
> /    forc_conv_thr=1e-5/
> /    prefix='Hf',/
> /    pseudo_dir='/potential'/
> /    outdir='./tmp/',/
> / //
> / &system/
> /    ibrav= 4,/
> /    a=3.6529/
> /   c=5.6544/
> /    nat=  3, ntyp= 2,/
> /    ecutwfc =50/
> /    vdw_corr='DFT-D',/
> / !   lspinorb=.true./
> / !   noncolin=.true./
> / !   ecutrho=300/
> / !   nbnd=14/
> /!    occupations='smearing'/
> /!    smearing='gaussian'/
> /!   degauss=0.01/
> / !  nspin=2/
> / !   starting_magnetization(1)=0.1/
> ///
> / &electrons/
> /    conv_thr=1e-12/
> /    mixing_beta = 0.7/
> ///
> / &ions/
> /    ion_dynamics = 'bfgs'/
> / //
> / &cell/
> /    cell_dynamics = 'bfgs'/
> //
> ///
> /ATOMIC_SPECIES/
> / Hf  95.94  Hf.pbe-mt_fhi.UPF/
> / S  32.065  S.pbe-mt_fhi.UPF/
> /ATOMIC_POSITIONS (crystal)/
> /Hf      -0.000000000  -0.000000000  -0.000000000/
> /S        0.666666667   0.333333333   0.257234636/
> /S        0.333333333   0.666666667  -0.257234636/
> / K_POINTS automatic/
> /10 8 8 0 0 0/
>
> The relaxed lattice structure is the one included in this input file 
> (I first did the full relaxation after which I copied the resulting 
> relaxed lattice structure into this input file, then modified this 
> file to compute electronic structure and phonons). The forces acting 
> on atoms are small and I believe this should be the equilibrium 
> structure of 1T-HfS2.
>
> /     Forces acting on atoms (Ry/au):/
> /
> /
> /     atom    1 type  1   force =     0.00000000 0.00000000    0.00000000/
> /     atom    2 type  2   force =     0.00000000 0.00000000   -0.00001404/
> /     atom    3 type  2   force =    -0.00000000 0.00000000    0.00001404/
> /
> /
> /     Total force =     0.000020     Total SCF correction =     0.000001/
> /
> /
> /
> /
> /     entering subroutine stress .../
> /
> /
> /          total   stress  (Ry/bohr**3)      (kbar)     P=   -0.16/
> /  -0.00000129  -0.00000000   0.00000000  -0.19     -0.00      0.00/
> /  -0.00000000  -0.00000129   0.00000000  -0.00     -0.19      0.00/
> /   0.00000000   0.00000000  -0.00000078 0.00      0.00     -0.12/
> /
> /
> *For cp.x, *I carefully follow the steps required to carry out a CP 
> simulations: Relax electronic structure to ground state -> Relax the 
> ion positions -> relax the cells. The input files are attached below.
>
> *Electronic relaxation*
> /&control/
> /    calculation='cp',/
> /    title='Halfnium disulfide'/
> /    restart_mode='from_scratch',/
> /    ndr=50,/
> /    ndw=50,/
> /    nstep=10000,/
> /    iprint=100/
> /    isave=100,/
> /    tstress = .true./
> /    tprnfor = .true./
> /    dt=10,/
> /    wf_collect=.true./
> /    etot_conv_thr=1e-6/
> /    forc_conv_thr=1e-3/
> /    ekin_conv_thr=1e-5/
> /    prefix='HfS2',/
> /    pseudo_dir='/home/jpeng/HfS2/potential'/
> /    outdir='./tmp/',/
> / //
> / &system/
> /    ibrav= 4,/
> /    a=3.6529/
> /   c=5.6544/
> /    nat=  3, ntyp= 2,/
> /    ecutwfc =50/
> /    vdw_corr='DFT-D',/
> / !   lspinorb=.true./
> / !   noncolin=.true./
> / !   ecutrho=300/
> / !   nbnd=14/
> /!    occupations='smearing'/
> /!    smearing='gaussian'/
> /!   degauss=0.01/
> / !  nspin=2/
> / !   starting_magnetization(1)=0.1/
> /! Hf  95.94  Hf.pbe-mt_fhi.UPF/
> /! S  32.065  S.pbe-mt_fhi.UPF/
> ///
> / &electrons/
> /    electron_dynamics='damp'/
> /!    electron_velocities='zero'/
> /    emass=400/
> /    emass_cutoff=1/
> /    electron_damping=0.1/
> ///
> / &ions/
> /    ion_dynamics = 'none'/
> / //
> / &cell/
> /    cell_dynamics = 'none'/
> //
> ///
> /ATOMIC_SPECIES/
> / Hf  95.94  Hf.pbe-mt_fhi.UPF/
> / S  32.065  S.pbe-mt_fhi.UPF/
> /ATOMIC_POSITIONS (crystal)/
> /Hf      -0.000000000  -0.000000000  -0.000000000/
> /S        0.666666667   0.333333333   0.257234636/
> /S        0.333333333   0.666666667  -0.257234636/
> / K_POINTS automatic/
> /10 8 8 0 0 0/
>
> Ion relaxation
> /&control/
> /    calculation='cp',/
> /    title='Halfnium disulfide'/
> /    restart_mode='restart',/
> /    ndr=50,/
> /    ndw=51,/
> /    nstep=50000,/
> /    iprint=100/
> /    isave=100,/
> /    tstress = .true./
> /    tprnfor = .true./
> /    dt=10,/
> /    wf_collect=.true./
> /    etot_conv_thr=1e-6/
> /    forc_conv_thr=1e-3/
> /    ekin_conv_thr=1e-5/
> /    prefix='HfS2',/
> /    pseudo_dir='/home/jpeng/HfS2/potential'/
> /    outdir='./tmp/',/
> / //
> / &system/
> /    ibrav= 4,/
> /    a=3.6529/
> /   c=5.6544/
> /    nat=  3, ntyp= 2,/
> /    ecutwfc =50/
> /    vdw_corr='DFT-D',/
> / !   lspinorb=.true./
> / !   noncolin=.true./
> / !   ecutrho=300/
> / !   nbnd=14/
> /!    occupations='smearing'/
> /!    smearing='gaussian'/
> /!   degauss=0.01/
> / !  nspin=2/
> / !   starting_magnetization(1)=0.1/
> /! Hf  95.94  Hf.pbe-mt_fhi.UPF/
> /! S  32.065  S.pbe-mt_fhi.UPF/
> ///
> / &electrons/
> /    electron_dynamics='damp'/
> /!    electron_velocities='zero'/
> /    emass=400/
> /    emass_cutoff=1/
> /    electron_damping=0.1/
> ///
> / &ions/
> /    ion_dynamics = 'damp'/
> /    ion_damping=0.1/
> /    ion_nstepe=10/
> / //
> / &cell/
> /    cell_dynamics = 'none'/
> //
> ///
> /ATOMIC_SPECIES/
> / Hf  95.94  Hf.pbe-mt_fhi.UPF/
> / S  32.065  S.pbe-mt_fhi.UPF/
> /ATOMIC_POSITIONS (crystal)/
> /Hf      -0.000000000  -0.000000000  -0.000000000/
> /S        0.666666667   0.333333333   0.257234636/
> /S        0.333333333   0.666666667  -0.257234636/
> / K_POINTS automatic/
> /10 8 8 0 0 0/
>
> Cell relaxation
> /&control/
> /    calculation='vc-cp',/
> /    title='Halfnium disulfide'/
> /    restart_mode='reset_counters',/
> /    ndr=51,/
> /    ndw=52,/
> /    nstep=50000,/
> /    iprint=100/
> /    isave=100,/
> /    tstress = .true./
> /    tprnfor = .true./
> /    dt=10,/
> /    wf_collect=.true./
> /    etot_conv_thr=1e-6/
> /    forc_conv_thr=1e-3/
> /    ekin_conv_thr=1e-5/
> /    prefix='HfS2',/
> /    pseudo_dir='/home/jpeng/HfS2/potential'/
> /    outdir='./tmp/',/
> / //
> / &system/
> /    ibrav= 4,/
> /    a=3.6529/
> /   c=5.6544/
> /    nat=  3, ntyp= 2,/
> /    ecutwfc =50/
> /    vdw_corr='DFT-D',/
> / !   lspinorb=.true./
> / !   noncolin=.true./
> / !   ecutrho=300/
> / !   nbnd=14/
> /!    occupations='smearing'/
> /!    smearing='gaussian'/
> /!   degauss=0.01/
> / !  nspin=2/
> / !   starting_magnetization(1)=0.1/
> /! Hf  95.94  Hf.pbe-mt_fhi.UPF/
> /! S  32.065  S.pbe-mt_fhi.UPF/
> ///
> / &electrons/
> /    electron_dynamics='damp'/
> /!    electron_velocities='zero'/
> /    emass=400/
> /    emass_cutoff=1/
> /    electron_damping=0.1/
> ///
> / &ions/
> /    ion_dynamics = 'damp'/
> /    ion_damping=0.1/
> /    ion_nstepe=10/
> / //
> / &cell/
> /    cell_dynamics = 'pr'/
> /!    cell_damping=0.1/
> /!    cell_dofree=volume/
> ///
> /ATOMIC_SPECIES/
> / Hf  95.94  Hf.pbe-mt_fhi.UPF/
> / S  32.065  S.pbe-mt_fhi.UPF/
> /ATOMIC_POSITIONS (crystal)/
> /Hf      -0.000000000  -0.000000000  -0.000000000/
> /S        0.666666667   0.333333333   0.257234636/
> /S        0.333333333   0.666666667  -0.257234636/
> / K_POINTS automatic/
> /10 8 8 0 0 0/
>
> The final equilibrium lattice structure obtained by cp.x is:
> **/ CELL_PARAMETERS/
> /    8.27944202   -3.49986616   -1.28541441/
> /    0.43381045    6.25063702   -0.26433640/
> /   -1.81611680   -0.30736678    9.28229385/
> /
> /
> /   System Density [g/cm^3] : 3.7550323993/
> /
> /
> /
> /
> /   System Volume [A.U.^3] : 477.6950599279/
> /
> /
> /
> /
> /   Center of mass square displacement (a.u.):  0.271737/
> /
> /
> /   Total stress (GPa)/
> /       -0.00003957         0.00000336  0.00017132/
> /        0.00000336        -0.00001393  0.00003875/
> /        0.00017132         0.00003875  0.00048005/
> /   ATOMIC_POSITIONS/
> /   Hf     -0.57392945538368E+00 -0.32523714658422E+00    
> -0.78842946683202E-01/
> /   S       0.61817237992192E+01  0.34715217744206E+01    
>  0.20852180260292E+00/
> /   S       0.31507619982481E+00  0.41860506478142E+01    
> -0.20961035507250E+01/
> /
> /
> /   ATOMIC_VELOCITIES/
> /   Hf     -0.49417894612947E-07 -0.41246570825668E-07    
> -0.28182774835127E-06/
> /   S       0.29443574450584E-06  0.17988901894696E-06    
>  0.34817154465079E-06/
> /   S      -0.14657506118618E-06 -0.56477323752712E-07    
>  0.49507043808484E-06/
> /
> /
> /   Forces acting on atoms (au):/
> /   Hf     -0.18727766763523E-03 -0.15291863668542E-03    
> -0.99976280595181E-03/
> /   S       0.33856074345196E-03  0.20689440901408E-03    
>  0.40153992932368E-03/
> /   S      -0.17602213243772E-03 -0.68887225779463E-04    
>  0.57298561574671E-03/
> /
> /
> A visualization is attached here
>
>
> while by pwscf, the equilibrium lattice structure is:
> /   CELL_PARAMETERS/
> /    6.90298059   -3.45149030    0.00000000/
> /    0.00000000    5.97815655    0.00000000/
> /    0.00000000    0.00000000   10.68526745/
> /
> /
> /   System Density [g/cm^3] : 4.0679453101/
> /
> /
> /
> /
> /   System Volume [A.U.^3] : 440.9499858676/
> /
> /
> /
> /
> /   Center of mass square displacement (a.u.):  0.000000/
> /
> /
> /   Total stress (GPa)/
> /       32.06481501        -0.01335027 -0.00956254/
> /       -0.01335027        32.07951164 -0.00592770/
> /       -0.00956139        -0.00592704  2.04176052/
> /   ATOMIC_POSITIONS/
> /   Hf      0.00000000000000E+00 -0.00000000000000E+00    
> -0.00000000000000E+00/
> /   S       0.34514902988605E+01  0.19927188491672E+01    
>  0.27486208819801E+01/
> /   S      -0.34514902047533E-08  0.39854377043125E+01    
> -0.27486208819801E+01/
> /
> /
> /   ATOMIC_VELOCITIES/
> /   Hf      0.00000000000000E+00  0.00000000000000E+00    
>  0.00000000000000E+00/
> /   S       0.00000000000000E+00  0.00000000000000E+00    
>  0.00000000000000E+00/
> /   S       0.00000000000000E+00  0.00000000000000E+00    
>  0.00000000000000E+00/
> /
> /
> /   Forces acting on atoms (au):/
> /   Hf      0.70847502228925E-03  0.43071957102166E-03    
> -0.17703368862259E-04/
> /   S      -0.52668423530029E-03 -0.28607208606422E-03    
> -0.81547327015321E-01/
> /   S      -0.41998284595312E-03 -0.22039679837681E-03    
>  0.81837284893753E-01/
>
> A visulization is attached below
>
>
>
> I am expecting some difference because pw.x uses DFT and BFGS 
> algorithm to relax the lattice structure while cp.x uses CP method, 
> but not so large a difference. Especially since the lattice structure 
> given by pw.x agrees with experiments and other published works, I am 
> suspecting is it because I have not correctly carried out variable 
> cell CP simulations.
>
> Can anyone help me understand the discrepancy I see in the results 
> produced by pw.x and cp.x code? Or pointing out any mistake I have 
> made during my simulations?
>
> Thank you in advance for your help, sincerely!
>
> Best
> Jie
> -- 
> ------------------------------------------------------------------------------------------------------------------------
> Jie Peng
> PhD student
> 2134 Glenn Martin Hall, Mechanical Engineering, University of Maryland
> College Park, Maryland, USA
> Phone:(+1) 240-495-9445
> Email: jiepeng at umd.edu <mailto:jiepeng at umd.edu>
>
>
>
> _______________________________________________
> users mailing list
> users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

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