[CP2K:9583] convergence problems when melting SiC at high pressure

[Fernan Saiz]

Hi,
Sorry for the confusion, I meant that after a few hundred MD steps, the SCF
is not converging anymore.

At the 800th MD step, just 200 MD steps before the SCF does not converge,
the band gap is 0.035644 eV at a pressure of 11.76 GPa. The pressure stays
between around 5 and 15 GPa between the initial step and before the SCF
starts not converging. At the 1000th MD step, when the SCF starts to not
converging, the band gap is -0.026438 eV with a pressure that drops to
-84.83 GPa. Please note that CP2k with PADE understimates the experimental
band gap for the beta-SiC with a value of 0.991279 eV.

Thanks,

- Fernan

On Tue, Oct 24, 2017 at 5:15 PM, <hut... at chem.uzh.ch> wrote:

> Hi
>
> is that the band gap of your system at that pressure?
>
> Also, you say "the ab-initio molecular dynamics at NVE does not converge
> after several hundred steps"
> Does that mean, after several hundred MD steps, the SCF is not converging
> anymore,
> or the SCF did not converge within several hundred steps?
>
> regards
>
> Juerg Hutter
> --------------------------------------------------------------
> Juerg Hutter                         Phone : ++41 44 635 4491
> Institut für Chemie C                FAX   : ++41 44 635 6838
> Universität Zürich                   E-mail: hut... at chem.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
>
> -----cp... at googlegroups.com wrote: -----
> To: cp... at googlegroups.com
> From: Fernan Saiz
> Sent by: cp... at googlegroups.com
> Date: 10/24/2017 05:14PM
> Subject: Re: [CP2K:9582] convergence problems when melting SiC at high
> pressure
>
> Hi,
> The band gap of beta-SiC is 2.36 eV. What are parameters could be adjusted?
>
> Thanks,
>
> - Fernan
>
> On Tue, Oct 24, 2017 at 8:46 AM,  <hut... at chem.uzh.ch> wrote:
> Hi
>
>  what do you expect for the band gap of this system?
>  For small band gap systems you might need to adjust
>  your simulation methods.
>
>  regards
>
>  Juerg Hutter
>  --------------------------------------------------------------
>  Juerg Hutter                         Phone : ++41 44 635 4491
>  Institut für Chemie C                FAX   : ++41 44 635 6838
>  Universität Zürich                   E-mail: hut... at chem.uzh.ch
>  Winterthurerstrasse 190
>  CH-8057 Zürich, Switzerland
>  ---------------------------------------------------------------
>
>  -----cp... at googlegroups.com wrote: -----
>  To: cp2k <cp... at googlegroups.com>
>  From: Fernan Saiz
>  Sent by: cp... at googlegroups.com
>  Date: 10/22/2017 08:34PM
>  Subject: [CP2K:9574] convergence problems when melting SiC at high
> pressure
>
>  Hello,
>  I am studying the melting of a 256-atom SiC system at high pressures
> using the Z-method. I face the problem that when the pressure is around 10
> o 20 GPa (obtained by reducing 1% the simulation cell size), the ab-initio
> molecular dynamics at NVE does not converge after several hundred steps. I
> tried reducing the timestep to 0.05 fs with a cutoff of 800 Ry for an
> initial temperature of 9000 K, which after a few hundred steps goes down to
> to some 4000 K and the system starts to melt. However, this system does not
> converge even though I used the CG minimizer with a eps_max 1.0E-6 for the
> inner and outer loops, the preconditioner FULL_ALL with the PADE
> functional. Input script file is attached.
>
>  I was wondering if I could receive any useful piece of advice.
>
>  Best regards,
>   - Fernan Saiz
>  Department of chemistry
>  Imperial College London
>
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>  [attachment "sic.inp" removed by Jürg Hutter/at/UZH]
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