[Pw_forum] how to consider the "dt" flag during vc-relax calculations

[Chaohao Hu]

Dear Pwscf users,

I want to perform a vc-relax calculation for a low-symmetry structure (P-1),
but the calculation is not always convergenced. Maybe this structure is far
away from its equilibrium. From the help files I know the time step flag
"dt"  is a important parameter for variable cell relaxing calculation. In
the manual, it is said the good values of "dt" is 50/70 or 100/150, but the
default value in INPUT_PW file is 20.0D0. How to understand them?  Here, a
part of my input file is attached. The initial atomic position is determined
by performing "relax" calculation.

&CONTROL
   calculation =   "vc-relax"   ,
   restart_mode = 'from_scratch' ,
   outdir='~/tmp/' ,
   pseudo_dir = '~/espresso32/pseudo' ,
   disk_io = 'default' ,
   verbosity = 'default' ,
   tstress = .true. ,
   tprnfor = .true. ,
   nstep =  55  ,
               etot_conv_thr = 1.0E-5  ,
               forc_conv_thr = 1.0D-4 ,
                          dt = 50 ,
/
&SYSTEM
  ibrav     = 0,
  celldm(1) = 12.2409,
  nosym     = .true.,
  nat       = 30,
  ntyp      = 3,
  ecutwfc   = 25.D0,
  ecutrho   = 150.D0,
/
&ELECTRONS
  electron_maxstep = 500,
  conv_thr    = 1.D-7,
  mixing_beta = 0.7D0,
  diagonalization   =   'david'   ,
/
&IONS
/
&CELL
  cell_dynamics = 'damp-w',
          press = 0.00,
      wmass = 0.007,
/
...
...
K_POINTS automatic
5 5 5 1 1 1

Best regards,
C. H. Hu

-- 
============================
C.H. Hu
Postdoctoral fellow
Chimie et Physico-Chimie appliquees
Institut Francais du Petrole (IFP)
Rueil-Malmaison, France
E_mail: chaohao.mse at gmail.com
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