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

[Cococcioni Matteo]

Dear Jibiao,

I don’t know whether this is the source of your problem, but your ecutrho seems a little low. Typically for US PPs it is 8 or 10 times bigger than ecutrho. Yours is barely above 4x. This is particularly important if your Se PP has d states. Have you studied the convergence of forces and stresses with ecutrho?

Best,

Matteo


On Nov 23, 2018, at 10:32 AM, jibiaoli <jibiaoli at foxmail.com<mailto:jibiaoli at foxmail.com>> wrote:

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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************************************************
Matteo Cococcioni
Theory and Simulation of Materials
École Polytechnique Fédérale de Lausanne






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