[Pw_forum] vc-relax (not orthogonal operation)

[Sohail Ahmad]

Dear QE users,
I am using vc-relax first time to get the optimised structure of MoS2 monolayer.
I believe the symmetry is breaking in the second step due to relaxation in x and y direction it is changing the number of k-points. 

What is the solution ??? (Somebody suggested a bigger cell with orthorhombic cell)
But HOW and WHY ???

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     Error in routine checkallsym (2):
     not orthogonal operation
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     stopping ...
-----------------------------------------------------------------------------------------------------------------------
input file as below

&control
  calculation = 'vc-relax',
  restart_mode = 'from_scratch',
  etot_conv_thr = 1.0d-5,
  forc_conv_thr = 1.0d-4,
  tstress = '.true.',
  tprnfor = '.true.,
  prefix = 'MoSml',
  pseudo_dir = '/home/sohail/Espresso/espresso-5.0.1/pseudo',
  outdir = './OUT',
/
&system
  ibrav = 4, a = 3.16, b = 3.16, c = 15, cosac = 0.0, cosbc = 0.0, cosab = -0.5,
  nat = 3, ntyp = 2,
  ecutwfc = 70,
  ecutrho = 300,
  nbnd = 26,
  occupations = 'smearing', smearing = 'gaussian', degauss = 0.001,
  nspin = 2,
  starting_magnetization(1) = 0.1d0,
/
&electrons
  mixing_beta = 0.7d0,
  conv_thr = 1.0d-15,
  electron_maxstep = 500,
/
&ions
 ion_dynamics = 'bfgs',
/
&cell
 cell_dynamics = 'bfgs',
 press = 0.d0,
 press_conv_thr = 1.2d0,
 cell_dofree = 'xy',
 /
ATOMIC_SPECIES
Mo  95.96  Mo.pw91-n-van.UPF
S   32.06  S.pw91-van_ak.UPF
ATOMIC_POSITIONS {Angstrom}
Mo  -0.000000016  1.824426860  3.072500000
S    1.580000016  0.912213416  1.474800000
S    1.580000016  0.912213416  4.670200000
K_POINTS {AUTOMATIC}
8 8 1 0 0 0


Thanks
Sohail Ahmad
King Khalid University
Abha, Saudi Arabia