[Pw_forum] structure oscillating with vc-md

[Stefano de Gironcoli]

Dear Amin Torabi
   you are performing a variable-cell MD simulation therefore the 
enthalpy is not minimized by the Newton equations for atoms+cell are 
integrated to give you the dynamics around the target pressure (P=0 in 
your case).
   to get the relaxation you should use calculation = "vc-relax" and 
then choose the minimization strategy.
   the default is bfgs but also damp dynamics is available.
   check the relevant input variables: ion_dynamics and cell_dynamics.

   best regards,
stefano


On 10/28/2011 02:49 AM, Amin Torabi wrote:
> Dear QE users,
>
> Will you please do me a favor and take a look at my input file, below.
> The total energy and force do not converge and keep oscillating...
> I have tried different dt (between 20-70) and wmass, and still not able to
> relax the structure
> Any comment on my the input_cards here (k-point,ecut,pp,conv...?)
>
> Many thanks
>
>
>
> &CONTROL
>          calculation     = 'vc-md'
>          pseudo_dir      = './'
>          outdir          = './'
>          prefix          = 'dt20'
>          tstress         = .true
>          tprnfor         = .true
>          nstep           = 100
>          dt              = 20
> /
> &SYSTEM
>          ibrav           = 12
>          celldm(1)       = 8.3147
>          celldm(2)       = 1.3
>          celldm(3)       = 1.4772
>          celldm(4)       = -0.260
>          nat             = 16
>          ntyp            = 2
>          ecutwfc         = 85
>          ecutrho         = 1100
>          input_dft       = 'pbesol'
>          nosym           = .true
> /
> &ELECTRONS
>          conv_thr        = 1.0D-9
> /
> &IONS
>          pot_extrapolation='second-order'
>          wfc_extrapolation='second-order'
>          ion_temperature = 'rescaling'
>          tempw           = 300
> /
> &CELL
>          press           = 0
>          cell_dynamics   = 'w'
>          wmass           = 4.2
> /
> ATOMIC_SPECIES
>   B  10.811    B.pbe-n-van.UPF
>   H  1.00794   H.pbe-van_bm.UPF
> ATOMIC_POSITIONS crystal
> B        0.005259620   0.145596712   0.040564862
> H       -0.199830030   0.176142715   0.150841828
> H        0.217291388   0.312290957  -0.013967013
> H        0.124960907  -0.022012847   0.122883862
> B       -0.005259620  -0.145596712  -0.040564862
> H        0.199830030  -0.176142715  -0.150841828
> H       -0.217291388  -0.312290957   0.013967013
> H       -0.124960907   0.022012847  -0.122883862
> B        0.494739818   0.354404554   0.540568678
> H        0.699828966   0.323861788   0.650847745
> H        0.282707973   0.187708799   0.486039576
> H        0.375038882   0.522017144   0.622882523
> B        0.505260182   0.645595446   0.459431322
> H        0.300171034   0.676138212   0.349152255
> H        0.717292027   0.812291201   0.513960424
> H        0.624961118   0.477982856   0.377117477
> K_POINTS automatic
>   8 8 8  0 0 0
>
>
>
>
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