[QE-users] Large difference between lattice structure simulated by pwscf code and cp.x code
Stefano Baroni
baroni at sissa.it
Thu Apr 5 20:02:09 CEST 2018
not “unphysical” just inaccurate … SB
> On 5 Apr 2018, at 19:39, Jie Peng <jiepeng at umd.edu> wrote:
>
> Stefano:
>
> I think that is right on the spot! Let me do a calculation using Gamma point only in pwscf and then compare again.
>
> So for cp.x, in order to get an accurate lattice structure, one would have to use a n*n*n supercell instead of a unit cell since it can only process real wavefunctions that are located at Gamma point only. Computations done on a single unit cell using cp.x code, therefore usually produces results that are unphysical. Is this the correct way to interpretate?
>
> Thank you very much!
>
> Best
> Jie
>
> On Thu, Apr 5, 2018 at 2:22 AM, Stefano de Gironcoli <degironc at sissa.it <mailto:degironc at sissa.it>> wrote:
> 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
>> <image.png>
>>
>> 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
>> <image.png>
>>
>>
>> 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>
>>
>>
>>
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> --
> ------------------------------------------------------------------------------------------------------------------------
> 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>
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