[Pw_forum] structure oscillating with vc-md

[Amin Torabi]

Dear Stefano,
I actually was able to relax it using vc-relax; however, I was curious to
see what happens with vc-md and vc-cp, mostly because I could set
temperature with vc-md and vc-cp and not with vc-relax.

Do you think it worth trying with vc-cp? i.e. does vc-cp render more
accurate structure, especially if I increase pressure?

Thanks in advance!

On Thu, Oct 27, 2011 at 11:52 PM, Stefano de Gironcoli <degironc at sissa.it>wrote:

> **
> 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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-- 
Amin Torabi
Ph.D. Student
Chemistry Department
The University *of* Western Ontario
London, On Canada, N6A 5B7
Phone: 519-661-2111 Ext: 87871
****************************************
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