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: jiep...@umd.edu
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