[Pw_forum] vc-relax convergence

[Manu Hegde]

Hello,

I am trying to optimize anatase TiO2 supercell with 48 atoms. The supercell
converges in 15 BFGS cycles for a perfect cell. But when I introduce defect
(by removing one of the oxygen atom), the vc-relax is not t all converging.
I am using the same parameters in both the cases. Can anyone give some
feedback on this.?.  Here is my input,


&control
                 calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = '/work/mhegde/tmp_tiodef/',
                  pseudo_dir = '/home/mhegde/tio_project/def_tio/',
                      prefix = 'tioan',
                   verbosity = 'high',

 /
 &system
                       ibrav = 0,
                       nat = 47,
                        ntyp = 2,
                     ecutwfc =40,
                     ecutrho=400,
                     occupations='smearing',
                      degauss=0.003

 /
 &electrons
                    conv_thr = 1.D-6,
                    mixing_beta=0.1
/
&ions
                    ion_dynamics='bfgs'

/
&cell
                    cell_dynamics='bfgs'

/
ATOMIC_SPECIES
   Ti  47.867000  Ti.pw91-nsp-van.UPF
   O   15.99900   O.pw91-van_ak.UPF

ATOMIC_POSITIONS angstrom
Ti       0.00000000       2.84182500       1.20970000
Ti       1.89455000       2.84182500       3.62910000
O        0.00000000       0.94727500       1.99939216
O        0.00000000       2.84182500       4.41879216
O        1.89455000       0.94727500       2.83940784
Ti      -1.89455000       0.94727500      -3.62910000
Ti       0.00000000       0.94727500      -1.20970000
O       -1.89455000      -0.94727500      -2.83940784
O       -1.89455000       0.94727500      -0.42000784
O        0.00000000      -0.94727500      -1.99939216
O        0.00000000       0.94727500      -4.41879216
Ti       0.00000000      -0.94727500       1.20970000
Ti       1.89455000      -0.94727500       3.62910000
O        0.00000000      -2.84182500       1.99939216
O        0.00000000      -0.94727500       4.41879216
O        1.89455000      -2.84182500       2.83940784
O        1.89455000      -0.94727500       0.42000784
Ti      -1.89455000      -2.84182500      -3.62910000
Ti       0.00000000      -2.84182500      -1.20970000
O       -1.89455000       2.84182500      -2.83940784
O       -1.89455000      -2.84182500      -0.42000784
O        0.00000000       2.84182500      -1.99939216
O        0.00000000      -2.84182500      -4.41879216
Ti      -3.78910000       2.84182500       1.20970000
Ti      -1.89455000       2.84182500       3.62910000
O       -3.78910000       0.94727500       1.99939216
O       -3.78910000       2.84182500       4.41879216
O       -1.89455000       0.94727500       2.83940784
O       -1.89455000       2.84182500       0.42000784
Ti       1.89455000       0.94727500      -3.62910000
Ti      -3.78910000       0.94727500      -1.20970000
O        1.89455000      -0.94727500      -2.83940784
O        1.89455000       0.94727500      -0.42000784
O       -3.78910000      -0.94727500      -1.99939216
O       -3.78910000       0.94727500      -4.41879216
Ti      -3.78910000      -0.94727500       1.20970000
Ti      -1.89455000      -0.94727500       3.62910000
O       -3.78910000      -2.84182500       1.99939216
O       -3.78910000      -0.94727500       4.41879216
O       -1.89455000      -2.84182500       2.83940784
O       -1.89455000      -0.94727500       0.42000784
Ti       1.89455000      -2.84182500      -3.62910000
Ti      -3.78910000      -2.84182500      -1.20970000
O        1.89455000       2.84182500      -2.83940784
O        1.89455000      -2.84182500      -0.42000784
O       -3.78910000       2.84182500      -1.99939216
O       -3.78910000      -2.84182500      -4.41879216

K_POINTS {automatic}

 2 2 2   0 0 0

CELL_PARAMETERS angstrom

 7.57820000       0.00000000       0.00000000
 0.00000000       7.57820000       0.00000000
 0.00000000       0.00000000       9.67760000

Thanks,
Manu
(University of Waterloo)
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