[Pw_forum] Temperature continuously going down in cp.x run

[vega lew]

Dear Uli,

Thank you for your time.

I'll read it and try to find more reasonable dt and emass.

Could you please tell me more about how to choose a suitable frequencies for
thermostat?

best,

vega

On Fri, Nov 27, 2009 at 7:32 AM, Uli Aschauer <aschauer at princeton.edu>wrote:

> Dear Vega,
>
> Your choice of dt=10 seems a bit large to me for dynamics. You will have to
> find a good value of dt combined with emass (for which you take the default
> value of 400) to conserve the energy in your system. To understand what this
> is all about I would suggest you to read at least the relevant section
> (2.4.4) herein: http://www.fz-juelich.de/nic-series/Volume1/marx.pdf
>
> For the Nose thermostat you not only set the target temperature but also
> the frequency. The default may be completely out of the range of the
> frequencies you try to excite in your system. As Paolo suggested, you will
> almost certainly have to tune the Nose parameters to get effective
> thermostatting.
>
> As for the amplitude of the randomization it does not really matter all
> that much. You will just spend a lot less computer time if you choose a
> value to give you something close to the temperature you want. You can
> randomize a few different amplitudes and then run dynamics without
> thermostat to see what temperature you converge to after a few hundred steps
> (given your dynamics is setup correctly). This allows you to make sort of a
> calibration of the temperature as a function of the randomization amplitude
> for your system.
>
> Best regards,
> -uli
>
> _________________________________________________________
> Uli Aschauer
> Princeton University
> Chemistry Department
> Frick Laboratory, Room 213
> Princeton, NJ 08544
> Tel: +1-609-258-0116
> Email: aschauer at princeton.edu
> _________________________________________________________
>
> On 27.11.2009, at 04:10, vega lew wrote:
>
> dear all,
>
> I want to calculate certain heterogeneous reaction on a solid surface.
> First input the initial structure from previous pw.x relaxations.
> Second I fixed ions and let electron damping calculation run;
> Then un-fixed the ions and let both electron  and ions damping calculations
> run.
> Third I gave a random motion to the atoms in the system with amprp(1)~(3) =
> 0.01
> and then repeated second step to bring the system to the ground state.
> Fourth I added temperature (300K) to the system, using verlet schedule.
>
> But the temperature continuously going down, from 1000K to 150K during the
> fisrt 3000 steps.
> I think there might be something wrong with my cp.x calcuation.
> Do you think the amprp(1)~(3) = 0.01 of random motion is too small?
>
> Here is the input of my dynamics process,
>  &CONTROL
>
>                        title = 'CP'
> ,
>                  calculation = 'cp'
> ,
>                 restart_mode = 'restart'
> ,
>                       outdir = '/disk5/nanjing/vega/cp/300/' ,
>                       wfcdir = '/tmp/'
> ,
>                   pseudo_dir =
> '/home/software/nanjing/vega/espresso-4.0.1/pseudo/' ,
>                       prefix = 'cp_molecular' ,
>                        nstep = 99999 ,
>                           dt = 10,
>                       iprint = 5,
>                        isave =
> 150,
>  /
>
>  &SYSTEM
>
>                        ibrav =
> 8,
>                    celldm(1) =24.8624,
>                    celldm(2) = 0.8520,
>                    celldm(3) = 1.6964,
>                          nat =
> 147,
>                         ntyp = 3,
>                         nr1b = 20,
>                         nr2b = 20,
>                         nr3b = 20,
>                         nbnd =
> 630,
>                    ecutwfc   =   30,
>                    ecutrho   =  300,
>  /
>
>
>  &ELECTRONS
>            electron_dynamics = 'verlet',
>  /
>
>  &IONS
>
>                 ion_dynamics = 'verlet'
>              ion_temperature = 'nose',
>                        tempw = 300,
>  /
> ..................
> ..................
>
> best wishes,
>
> vega
>
> --
>
> ==================================================================================
> Vega Lew ( weijia liu)
> Graduate student
> State Key Laboratory of Materials-oriented Chemical Engineering
> College of Chemistry and Chemical Engineering
> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
>
> ******************************************************************************************************************
> Email: vegalew at gmail.com
> Office: Room A705, Technical Innovation Building, Xinmofan Road 5#,
> Nanjing, Jiangsu, China
> ******************************************************************************************************************
>
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-- 
==================================================================================
Vega Lew ( weijia liu)
Graduate student
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
******************************************************************************************************************
Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
Jiangsu, China
******************************************************************************************************************
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