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These days, I'm having a trouble in atomic relaxing of "EuTiO3" with tetragonal symmetry using Quantum espresso 7.1 for a period of more that a week. This material have a transverse optical mode to z-axis("001" direction). So, I try to relax this material along the z-axis. My order of relaxing the EuTiO3 is as follows:

  1. I download "cif.file" including the atomic position & lattice from "Materials Explorer( https://next-gen.materialsproject.org/materials ) "

  2. At Quantum espresso, "vc-relax(lattice realxation)" this material.

  3. "Relax" this material along the z-axis(= the direction of transverse optical mode,001).

At "2" process, total energy is decreased. But at "3" process, total energy is oddly increased!!. By other paper related EuTiO3, because this material is unstable to the direction of "z-axis", total energy should be also decreased at "3" process. I don't know what the reason is.

At similar structure "SrTiO3" with tetragonal symmetry , this problem didn't occur. At "SrTiO3", the same procedure as above was performed, but total energy was decreased at both "2" & "3" process.

Both "EuTiO3" & "SrTiO3" are perovskite material. One difference is that "EuTiO3" have antiferromagnetic property(=spin polarization) unlike "SrTiO3". Hence, I specified the "magnetization" and "Hubbard potential" to the input data of "EuTiO3"( In another paper, I know that magnetization and Hubbard potential are specified when relaxing EuTiO3 material.) Did I typed the "magnetization" & "Hubbard potential" data wrong? Please help me. I need sincere help from experts.

P.S I add my input data of "EuTiO3" entered into Quatum Espresso.

  1. process : "vc-relax"

&control calculation = 'vc-relax' restart_mode='from_scratch', prefix='ETO', pseudo_dir ='/home/dydtlr5506/pseudo', outdir='./wavefunc' tstress = .true. forc_conv_thr = 1.0d-7 dt = 20 disk_io = 'none' nstep =9910 / &system ibrav= 0, nat=20, ntyp= 4, ecutwfc = 80.0, ecutrho = 640.0, occupations = 'smearing', smearing = 'gaussian' degauss = 0.0010 nspin = 2 starting_magnetization(1)=7.0 starting_magnetization(2)=-7.0

/ &electrons mixing_mode = 'plain' electron_maxstep = 100 conv_thr = 1.0d-13
/ &ions ion_dynamics = 'bfgs' / &cell cell_dofree='xyz' cell_dynamics = 'bfgs' / ATOMIC_SPECIES Eu1 151.964 Eu.pbe-spdfn-kjpaw_psl.1.0.0.UPF Eu2 151.964 Eu.pbe-spdfn-kjpaw_psl.1.0.0.UPF Ti 47.86 Ti.pbe-spn-kjpaw_psl.1.0.0.UPF O 15.999 O.pbe-n-kjpaw_psl.1.0.0.UPF K_POINTS {automatic} 6 6 4 0 0 0 CELL_PARAMETERS (angstrom) 5.510044859 0.000000000 0.000000000 0.000000000 5.510044859 0.000000000 0.000000000 0.000000000 7.871680636 ATOMIC_POSITIONS (crystal) Eu1 0.0000000000 0.5000000000 0.2500000000 1 1 0 Eu2 0.5000000000 0.0000000000 0.2500000000 1 1 0 Eu1 0.5000000000 0.0000000000 0.7500000000 1 1 0 Eu2 0.0000000000 0.5000000000 0.7500000000 1 1 0 Ti 0.5000000000 0.5000000000 0.5000000000 1 1 0 Ti 0.0000000000 0.0000000000 0.5000000000 1 1 0 Ti 0.0000000000 0.0000000000 0.0000000000 1 1 0 Ti 0.5000000000 0.5000000000 0.0000000000 1 1 0 O 0.5000000000 0.5000000000 0.2500000000 1 1 0 O 0.0000000000 0.0000000000 0.2500000000 1 1 0 O 0.7183286073 0.2183286073 0.0000000000 1 1 0 O 0.7816713921 0.2816713922 0.5000000000 1 1 0 O 0.2816713922 0.2183286079 0.5000000000 1 1 0 O 0.2183286073 0.2816713927 0.0000000000 1 1 0 O 0.0000000000 0.0000000000 0.7500000000 1 1 0 O 0.5000000000 0.5000000000 0.7500000000 1 1 0 O 0.2183286079 0.7183286078 0.5000000000 1 1 0 O 0.2816713927 0.7816713927 0.0000000000 1 1 0 O 0.7816713927 0.7183286073 0.0000000000 1 1 0 O 0.7183286078 0.7816713921 0.5000000000 1 1 0 HUBBARD (ortho-atomic) U Eu1-4f 5.9 U Eu2-4f 5.9 enter image description here 2. process: output total energy = -5712.21091180 Ry

  1. process : "relax"

&control calculation = 'relax' restart_mode='from_scratch', prefix='ETO', pseudo_dir ='/home/dydtlr5506/pseudo', outdir='./wavefunc' tstress = .true. forc_conv_thr = 1.0d-7 dt = 20 disk_io = 'none' nstep =9910 / &system ibrav= 0, nat=20, ntyp= 4, ecutwfc = 80.0, ecutrho = 640.0, ! nbnd =200 ! occupations = 'fixed', occupations = 'smearing', smearing = 'gaussian' degauss = 0.0010 nspin = 2 starting_magnetization(1)=0.5 starting_magnetization(2)=-0.5

! nosym = .true. ! nbnd = 120 ! nosym_evc = .true. ! noinv = .true. ! no_t_rev = .true. / &electrons mixing_mode = 'plain' electron_maxstep = 100 conv_thr = 1.0d-9
/ &ions ion_dynamics = 'bfgs' / &cell cell_dofree='xyz' cell_dynamics = 'bfgs'

/ ATOMIC_SPECIES Eu1 151.964 Eu.pbe-spdfn-kjpaw_psl.1.0.0.UPF Eu2 151.964 Eu.pbe-spdfn-kjpaw_psl.1.0.0.UPF Ti 47.86 Ti.pbe-spn-kjpaw_psl.1.0.0.UPF O 15.999 O.pbe-n-kjpaw_psl.1.0.0.UPF

K_POINTS {automatic} 6 6 4 0 0 0

CELL_PARAMETERS (angstrom) 5.505334716 -0.000000000 0.000000000 0.000000000 5.505334716 0.000000000 -0.000000000 -0.000000000 7.873593914

ATOMIC_POSITIONS (crystal) Eu1 0.0000000000 0.5000000000 0.2520000000 0 0 1 Eu2 0.5000000000 0.0000000000 0.2520000000 0 0 1 Eu1 0.5000000000 -0.0000000000 0.7520000000 0 0 1 Eu2 -0.0000000000 0.5000000000 0.7520000000 0 0 1 Ti 0.0000000000 0.0000000000 0.0040000000 0 0 1 Ti 0.5000000000 0.5000000000 0.0040000000 0 0 1 Ti 0.0000000000 0.0000000000 0.5040000000 0 0 1 Ti 0.5000000000 0.5000000000 0.5040000000 0 0 1 O 0.0000000000 0.0000000000 0.2470000000 0 0 1 O 0.5000000000 0.5000000000 0.2470000000 0 0 1 O -0.0000000000 0.0000000000 0.7470000000 0 0 1 O 0.5000000000 0.5000000000 0.7470000000 0 0 1 O 0.2179836940 0.2820163063 -0.0020000000 0 0 1 O 0.2820163063 0.7820163060 -0.0020000000 0 0 1 O 0.7179836937 0.2179836940 -0.0020000000 0 0 1 O 0.7820163060 0.7179836937 -0.0020000000 0 0 1 O 0.2179836608 0.7179836609 0.4970000000 0 0 1 O 0.2820163391 0.2179836608 0.4970000000 0 0 1 O 0.7179836609 0.7820163392 0.4970000000 0 0 1 O 0.7820163392 0.2820163391 0.4970000000 0 0 1

HUBBARD (ortho-atomic) U Eu1-4f 5.9 U Eu2-4f 5.9

enter image description here

  1. process: output total energy = -5711.56708785 Ry
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