[Pw_forum] cp.x stops exceeding the maximum number of iteration

[Максим Арсентьев]

Dear Rolly,

I'm not familiar with MD too, but tried it in SIESTA. I think you need to
have training with more simple and real systems so you can check your
results (e.g. melting temperature of the solid). Also ABINIT tutorial is
exceptionally detailed. Only after that you can proceed.
I had the same problem: I was need the ion to hop to vacancy but the system
was unadequate with parameters I used in SIESTA.

2016-12-30 12:13 GMT+04:00 Rolly Ng <rollyng at gmail.com>:

> Dear QE users,
>
> I am running MD with cp.x and I am trying to observe the trajectory of a
> molecule detaching from nickel-doped graphene surface.
>
> It started with the molecule attached to the nickel atom in graphene
> sheet, electron minimization and ionic minimization in cp.x completed
> successfully. I then added a small random displacement to the system.
> When this is done. I added the followings to my input files, tempw
> increased from 100K to 200K then 300K. I have set dt=1.0d0, which is the
> smallest time step I can get.
>
> &ELECTRONS
> emass = 400.d0 ,
> emass_cutoff = 2.5d0 ,
> electron_dynamics = 'verlet' ,
> /
>
> &IONS
> ion_dynamics = 'verlet' ,
> ion_temperature = 'nose' ,
> fnosep = 40.0 ,
> tempw = 100.0 ,
> /
>
> Each temperature was set to run for 10,000 time steps (100K, followed by
> 200K, then 300K with 'restart') which I believe equals to 0.24 fs. This
> is insufficient to obtain the trajectory, so I extended the 300K case to
> 50,000 time steps to get to 1.2 ps.
>
> But, cp.x failed at middle at about 18,000 time step, complaining
> maximum number of iteration is reached. I took a look at the .evp file
> and I saw the very last three lines produced strange numbers.
>
> #   nfi    time(ps)        ekinc        T_cell(K) Tion(K)
> etot               enthal econs               econt
> Volume        Pressure(GPa)
>    17920  4.334641E-01  4.408245E-01  0.000000E+00 2.906500E+02
> -736.06724803       -736.06724803 -735.93194407       -665.53445700
> 3.183024E+04       0.82843
>    17930  4.337060E-01  4.413418E-01  0.000000E+00 2.931947E+02
> -736.06864256       -736.06864256 -735.93215404       -665.53398181
> 3.183024E+04       0.80824
>    17940  4.339478E-01  4.415645E-01  0.000000E+00 2.960657E+02
> -736.07019548       -736.07019548 -735.93237041       -665.53381758
> 3.183024E+04       0.79642
>    17950  4.341897E-01  4.415359E-01  0.000000E+00 2.998132E+02
> -736.07295464       -736.07295464 -735.93338506       -665.53470772
> 3.183024E+04       0.86277
>    17960  4.344316E-01  4.419086E-01  0.000000E+00 3.037218E+02
> -736.07463932       -736.07463932 -735.93325017       -665.53404513
> 3.183024E+04       1.19960
>    17970  4.346735E-01  4.442741E-01  0.000000E+00 3.066442E+02
> -736.07570387       -736.07570387 -735.93295428       -665.53122014
> 3.183024E+04       3.46370
>    17980  4.349154E-01  5.721941E-01  0.000000E+00 3.111465E+02
> -736.07787056       -736.07787056 -735.93302506       -665.40319056
> 3.183024E+04      22.55459
>
> It seems the ekinc and pressure increased suddenly and the system became
> destabilized.
>
> How can I resolved the problem?
>
> Thanks,
> Rolly
>
> --
> PhD. Research Fellow,
> Dept. of Physics & Materials Science,
> City University of Hong Kong
> Tel: +852 3442 4000
> Fax: +852 3442 0538
>
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-- 
Best wishes,
Maxim Arsent'ev, Ph.D. (Chemistry)
Laboratory of research of nanostructures
Institute of Silicate Chemistry of RAS
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