[QE-users] Stress values from vc-relax and scf are different, but why?
Hsin-Yu Ko
hsin-yu.ko at cornell.edu
Sun Jun 19 16:22:00 CEST 2022
Hi Ted,
One possibility is that a fixed set of G-vector is selected using the initial cell based on the specified `ecutwfc`. This G-vector set is kept fixed during a vc-relax run (which can modify effectively the stored G-vectors through changes in the unit cell). As such, at the end of vc-relax, the planewave cutoff can differ from direct scf calculation if the unit cell undergoes sizable strain. One solution to this problem is to use the approach by M. Bernasconi et al, [J. Phys. Chem. Solids 56, 501 (1995), doi:10.1016/0022-3697(94)00228-2]. Relevant QE input parameters include: ecfixed, qcutz, and q2sigma see: https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm406
Hope that helps.
Hsin-Yu
--
Hsin-Yu Ko
Postdoctoral Research Fellow
Department of Chemistry and Chemical Biology
Cornell University
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of 杨腾 <yangteng at imr.ac.cn>
Sent: Sunday, June 19, 2022 1:51 AM
To: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: [QE-users] Stress values from vc-relax and scf are different, but why?
Dear QE users and experts,
I am pretty confused by the different outputed stress value from both
the vc-relax (the last step) and scf steps. Could you please help me
to figure out why. Thank you so much!
Ted
Here is the output stress from the last step of vc-relax:
total stress (Ry/bohr**3) (kbar) P= 0.01
0.00000028 -0.00000000 -0.00000013 0.04 -0.00 -0.02
-0.00000000 -0.00000011 -0.00000000 -0.00 -0.02 -0.00
-0.00000013 -0.00000000 0.00000011 -0.02 -0.00 0.02
and the output stress from scf:
total stress (Ry/bohr**3) (kbar) P= -417.74
-0.00286693 0.00000000 -0.00006361 -421.74 0.00 -9.36
0.00000000 -0.00279769 0.00000000 0.00 -411.55 0.00
-0.00006361 0.00000000 -0.00285453 -9.36 0.00 -419.92
The input files for vc-relax is as below:
---------------start of vc-relax.in---------------------
&CONTROL
calculation = 'vc-relax'
verbosity = 'high'
restart_mode = 'from_scratch'
wf_collect = .true.
nstep = 200
tstress = .true.
tprnfor = .true.
outdir = './'
prefix = 'NiP2-monoclinic'
etot_conv_thr = 1.0D-6
forc_conv_thr = 1.0D-5
pseudo_dir = '../../pp/'
!tefield = .true. !add saw-like potential
!dipfield = .true.
!lelfield = .true.
!nberrycyc = 5
!gdir = 3
!nppstr = 1
/
&SYSTEM
ibrav = 0
celldm(1) = 1.6896
!celldm(2) =
!celldm(3) = 9.5983431328106
nat = 12
ntyp = 2
!nbnd =
!tot_charge =
!tot_magnetization =
!starting_magnetization(1) =
!angle1(1) =
!angle2(1) =
ecutwfc = 120
ecutrho = 480 !if ncpp,stick to the 4* relation
!nr1 =
!nr2 =
!nr3 =
!nosym = .true.
!noinv = .true.
!no_t_rev = .true. ! disable the usage of magnetic symmetry operations
!occupations = 'fixed' ! set to 'tetrahedra' if calculate dos
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.01 ! check the smearing contribution to total energy and if it
! is large then try to lower the value
nspin = 1 ! 1:non-polarized 2: magnetization along z axis
!noncolin = .true. ! magnetization in generic direction,
!lspinorb = .true. ! soc calculation use a pseudopotential with spin-orbit.
!assume_isolated= '2D'
!input_dft = 'vdW-DF' ! defining the DFT functional
!nqx1 = 1 ! proportional to nk1; for hybrid functions
!nqx2 = 1 ! proportional to nk2
!nqx3 = 1 ! proportional to nk3
!lda_plus_u = .true.
!Hubbard_U(1) = 0
!Hubbard_U(2) = 0
!vdw_corr = 'DFT-D' ! Dispersion correction in vdw calculations
!edir = 3 ! This is the direction of applied field
!emaxpos = 0.95
!eopreg = 0.1
!eamp = 0.019446905 ! Amplitude of e-field 1a.u. = 51.4220632*10^10 V/m
/
&ELECTRONS
electron_maxstep = 1000
conv_thr = 1.0D-10
mixing_mode = 'plain'
!mixing_mode = 'local-TF'
mixing_beta = 0.5
diagonalization = 'david'
!diago_thr_init = 1.0D-13 ! for non-scf calculations
!diago_full_acc = .true.
!efield = 0.027502070 ! 1 a.u. = 36.3609*10^10 V/m
!efield_cart(1) = 0.0
!efield_cart(2) = 0.0
!efield_cart(3) = 0.027502070
!startingpot = 'file' !start from existing charge file
!startingwfc = 'file'
/
&IONS
ion_dynamics = 'bfgs'
upscale = 1.0D3
trust_radius_min = 1.0D-15
/
&CELL
cell_dynamics = 'bfgs'
press = 0
press_conv_thr = 0.01
cell_dofree = 'all'
/
CELL_PARAMETERS {alat}
6.210735282 -0.000000003 -0.228119407
-0.000000002 5.833791719 -0.000000015
-2.783178192 -0.000000013 5.154174308
ATOMIC_SPECIES
P 30.9737 P.pz-hgh.UPF
Ni 58.6934 Ni.pz-hgh.UPF
ATOMIC_POSITIONS {crystal}
P 0.2206418181 0.1125023368 0.3445362239
P 0.7793582199 0.8874976832 0.6554637631
P 0.7793582103 0.1125022767 0.1554637796
P 0.2206418107 0.8874977433 0.8445362534
P 0.7206419422 0.6125043167 0.3445270549
P 0.2793580398 0.3874957243 0.6554729321
P 0.2793580310 0.6125043756 0.1554729615
P 0.7206419340 0.3874956654 0.8445270715
Ni 0.2499621059 0.2500045449 -0.0000154609
Ni 0.7500379121 0.7499954551 0.0000154609
Ni 0.7500378821 0.2500044729 0.5000154429
Ni 0.2499621649 0.7499955271 0.4999845671
K_POINTS {automatic} !50 ! if molecular {gamma}
8 8 8 0 0 0
---------------end of vc-relax.in---------------------
And the scf input is as follows,
--------start of scf.in----------
&CONTROL
calculation = 'scf'
!verbosity = 'high'
restart_mode = 'from_scratch'
wf_collect = .true.
nstep = 200
tstress = .true.
tprnfor = .true.
outdir = './'
prefix = 'NiP2-monoclinic'
etot_conv_thr = 1.0D-6
forc_conv_thr = 1.0D-5
pseudo_dir = '../../pp/'
!tefield = .true. !add saw-like potential
!dipfield = .true.
!lelfield = .true.
!nberrycyc = 5
!gdir = 3
!nppstr = 1
/
&SYSTEM
ibrav = 0
celldm(1) = 1.88964475
!celldm(2) =
!celldm(3) = 9.5983431328106
nat = 12
ntyp = 2
!nbnd =
!tot_charge =
!tot_magnetization =
!starting_magnetization(1) =
!angle1(1) =
!angle2(1) =
ecutwfc = 120
ecutrho = 480 !if ncpp,stick to the 4* relation
!nr1 =
!nr2 =
!nr3 =
!nosym = .true.
!noinv = .true.
!no_t_rev = .true. ! disable the usage of magnetic symmetry operations
!occupations = 'fixed' ! set to 'tetrahedra' if calculate dos
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.01 ! check the smearing contribution to total energy and if it
! is large then try to lower the value
nspin = 1 ! 1:non-polarized 2: magnetization along z axis
!noncolin = .true. ! magnetization in generic direction,
!lspinorb = .true. ! soc calculation use a pseudopotential with spin-orbit.
!assume_isolated= '2D'
!input_dft = 'vdW-DF' ! defining the DFT functional
!nqx1 = 1 ! proportional to nk1; for hybrid functions
!nqx2 = 1 ! proportional to nk2
!nqx3 = 1 ! proportional to nk3
!lda_plus_u = .true.
!Hubbard_U(1) = 0
!Hubbard_U(2) = 0
!vdw_corr = 'DFT-D' ! Dispersion correction in vdw calculations
!edir = 3 ! This is the direction of applied field
!emaxpos = 0.95
!eopreg = 0.1
!eamp = 0.019446905 ! Amplitude of e-field 1a.u. = 51.4220632*10^10 V/m
/
&ELECTRONS
electron_maxstep = 1000
conv_thr = 1.0D-10
mixing_mode = 'plain'
!mixing_mode = 'local-TF'
mixing_beta = 0.5
diagonalization = 'david'
!diago_thr_init = 1.0D-13 ! for non-scf calculations
!diago_full_acc = .true.
!efield = 0.027502070 ! 1 a.u. = 36.3609*10^10 V/m
!efield_cart(1) = 0.0
!efield_cart(2) = 0.0
!efield_cart(3) = 0.027502070
!startingpot = 'file' !start from existing charge file
!startingwfc = 'file'
/
CELL_PARAMETERS {alat}
6.2577067603003895 0.0000000000000000 -0.0777025195301591
0.0000000000000000 5.5251065872474996 0.0000000000000000
-2.6753479058107592 0.0000000000000000 4.8473353267277162
ATOMIC_SPECIES
P 30.9737 P.pz-hgh.UPF
Ni 58.6934 Ni.pz-hgh.UPF
ATOMIC_POSITIONS (crystal)
P 0.2015645274872214 0.1129918772500652 0.3353648698544600
P 0.7984355105127818 0.8870081427499362 0.6646351171455352
P 0.7984354965127807 0.1129918772500652 0.1646351351455369
P 0.2015645244872176 0.8870081427499362 0.8353648978544624
P 0.7015644904872218 0.6129918982500636 0.3353648698544600
P 0.2984354915127767 0.3870081427499364 0.6646351171455352
P 0.2984354775127825 0.6129918982500636 0.1646351351455369
P 0.7015644874872180 0.3870081427499364 0.8353648978544624
Ni 0.2500000000000000 0.2500000000000000 -0.0000000000000000
Ni 0.7500000180000015 0.7500000000000000 -0.0000000000000000
Ni 0.7500000420000035 0.2500000000000000 0.5000000049999969
Ni 0.2500000049999969 0.7500000000000000 0.5000000049999969
K_POINTS {automatic} !50 ! if molecular {gamma}
8 8 8 0 0 0
--------end of scf.in------------
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