[QE-users] GET BUCKLING IN OPTIMIZATION

[Lorenzo Paulatto]

Hello,

if the initial position have high symmetry, the relaxation will not be 
able to break the symmetry. You need to break the symmetry by hand, by 
moving the atoms a bit, before relaxing in order to achieve a buckled 
structure.

kind regards

On 25/08/2025 20:31, Barsha Pal wrote:
> Hello everyone,
> I am trying to optimize a structure existing in literature. It is 
> reported to have buckling not planar. I made the pristine (only carbon 
> -- totally planar) analogue of the structure and doped it to my 
> target. Now on optimizing the z coordinates do not change at all. I 
> need the z to be changed as well to get the target buckling. Also the 
> optimization converged for a loose criteria
> ( energy convergence thresh.=  1.0E-05
>      force convergence thresh. =      1.0E-04
>      press convergence thresh. =      5.0E-03)
> and when I tighten the criteria, BFGS fails. I have tried optimizing 
> with and without cell_dofree = all and 2Dxy, but the z remains unchanged.
>
>
> The input specifications are:
>
> &CONTROL
>     calculation   = "vc-relax"
>     restart_mode  = "from_scratch"
>     outdir  = "/tmp/"
>     prefix  = "pwscf"
>     pseudo_dir  = "/p/"
>     verbosity     = "high"
>     etot_conv_thr = 1.0D-6
>     forc_conv_thr = 1.0D-5
>     nstep  = 1000
>     tprnfor  = .true.
>     disk_io  = "none"
> /
>
> &SYSTEM
>   ibrav     = 0
>   celldm(1)  = 14.629678225
>   nat        = 8
>   ntyp       = 2
>   ecutwfc    = 170
>   ecutrho    = 680
>   occupations = "smearing"
>   smearing = "mv"
>   degauss = 0.005
>
> /
>
> &ELECTRONS
>     electron_maxstep = 600
>     mixing_beta = 0.3
>     conv_thr =  1.0d-6
> /
>
> &IONS
>     ion_dynamics = "bfgs"
> /
>
> &CELL
>     press   =  0.0
>     cell_dynamics  = "bfgs"
>     cell_dofree   = "2Dxy"
> /
>
> ATOMIC_SPECIES
> A   000  A.pbe-dnl-kjpaw_psl.1.0.0.UPF
>  B  00  B.pbe-nl-kjpaw_psl.1.0.0.UPF
>
> CELL_PARAMETERS (alat=  14.629678225 )
>    1.000000000   0.000000000   0.000000000
>    0.000000000   1.000000000   0.000000000
>    0.000000000   0.000000000   2.583596722
>
> ATOMIC_POSITIONS (crystal)
> A              0.6470402285        0.1471007113  0.5000000000
> B                0.6491194122        0.8509186097  0.5000000000
> B               0.3508805878        0.1490813903  0.5000000000
> A              0.3529597715        0.8528992887  0.5000000000
> A             0.1471007113        0.3529597715  0.5000000000
> B                0.8509186097        0.3508805878  0.5000000000
> B                0.1490813903        0.6491194122  0.5000000000
> A             0.8528992887        0.6470402285  0.5000000000
>
> K_POINTS {automatic}
>   12 12 3 0 0 0
>
>
> NOTE: This is supposed to be a 2D surface with buckling and with a 
> band gap.
>
>
> Ashley Cooper
> Phd
>
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-- 
Dr. Lorenzo Paulatto
IR IMPMC - CNRS UMR 7590 / Sorbonne Université / MNHN
phone: +33 (0)1 442 79822 / telegram: lpaulatto
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
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