[QE-users] Unit Cell goes larger and larger in variable cell geometry optimization

[Zakaria Azdad]

Dear Li,


I had the same issue back in the days.If you start really far from equilibrium it is usually hard to get the ground state, the way I solved it is by running a scf for a set of celldm(1) and looking either at forces, pressure or the total energy.


Once the approximate value of celldm is found, I runned a relax calculation and than a vc-relax.


Hope this will work for you as well,


Cheers,


Zack

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of jibiaoli <jibiaoli at foxmail.com>
Sent: Friday, November 23, 2018 10:32:11 AM
To: users
Subject: [QE-users] Unit Cell goes larger and larger in variable cell geometry optimization

Dear QE users and developers,

Recently I used vc-relax to optimize Se in the honeycomb structure, but the unit cell goes larger and larger without convergence. To me there must be something wrong with my calculations. Do you have any idea to get everything right?

Best
Jibiao Li
Yangtze Normal University, China


 &CONTROL
                 calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = './' ,
                  pseudo_dir = '/home/jibiaoli/pseudo/' ,
                      prefix = 'Se_hc' ,
                     disk_io = 'high' ,
 /
 &SYSTEM
                       ibrav = 4,
                   celldm(1) = 4.7126,
                   celldm(3) = 8.41,
                         nat = 2,
                        ntyp = 1,
                     ecutwfc = 41 ,
                     ecutrho = 180 ,
                 occupations = 'smearing' ,
                     degauss = 0.05D0 ,
                    smearing = 'methfessel-paxton' ,
                    vdw_corr = 'grimme-d2' ,
 /
 &ELECTRONS
                 mixing_beta = 0.3D0 ,
             diagonalization = 'david' ,
 /
 &IONS
                ion_dynamics = 'bfgs' ,
 /
 &CELL
               cell_dynamics = 'bfgs' ,
                 cell_dofree = '2Dxy' ,
 /
ATOMIC_SPECIES
   Se   78.96100  Se.pbe-van.UPF
ATOMIC_POSITIONS angstrom
   Se      1.246899765    0.719897900    0.000000000
   Se      0.000000000    0.000000000    0.000000000     0 0 0
K_POINTS automatic
  9 9 1   0 0 0

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