[Pw_forum] How to set the ensemble when doing molecule

[Axel Kohlmeyer]

On Mon, Jun 8, 2009 at 9:53 PM, Lu Yunhao<phylyh at nus.edu.sg> wrote:
> If I set ion_temperature= 'not_controlled', the tempw is still used and
> meaningful?

yes. it will set the initial temperature.

> I attach part of my input file as follows. Is it right? By the way, I add
> electric field along Z direction.

if you add an electric field, you _don't_ do an NVE ensemble
by not controlling the temperature. the external field will create
energy, i.e. you'll have a non-equilibrium system.

>
> &CONTROL
>                 title = 'MD-contT' ,
>                 calculation = 'md' ,
>                prefix='MD-contT',
>                restart_mode = 'from_scratch' ,
>                 tefield=.true.,
>                  outdir = '/home/phylyh/Au_gr-check/MD-contT/tmp' ,
>                  pseudo_dir = '/home/phylyh/pseudo_dir' ,
>                 dt=40,
>                 nstep=500,
> &IONS
>    ion_dynamics='verlet',
>    ion_temperature='rescale-v',
>    tempw=300.D0,
>    nraise=1,
>    tolp=100,

if you use rescale and tolp, you are not in a defined ensemble
either. since you remove or add energy to your system in an
arbitrary way.

cheers,
   axel.

>    pot_extrapolation='second-order',
>    wfc_extrapolation='second-order'
> /
>
>
>
> Message: 5
> Date: Sat, 06 Jun 2009 10:37:16 -0400
> From: Axel Kohlmeyer <akohlmey at cmm.chem.upenn.edu>
> Subject: Re: [Pw_forum] How to set the ensemble when doing molecule
>        dynamics calculation with pw.x
> To: PWSCF Forum <pw_forum at pwscf.org>
> Message-ID: <1244299036.3912.9870.camel at zero>
> Content-Type: text/plain
>
> On Sat, 2009-06-06 at 20:13 +0800, Lu Yunhao wrote:
>> Dear All
>
>> Can the pw.x code do molecule dynamic calculation with NVE ensemble?
>
> yes, of course!
>
>> I search the Manu and can not find any descriptions about ensemble.
>
> well, all you have to do is to a) have a constant number of atoms,
> b) a constant volume, and c) _not_ control the temperature.
>
> a) is trivial (you cannot add or remove atoms anyways)
> b) is simple, too (this is the default)
> c) only requires a look at the documentation of the &ions
>   namelist. check out "tempw"
>
>
> it cannot get much simpler.
>    axel.
>>
>>
>> Best wishes,
>>
>> Yunhao
>>
>> Resear Fellow
>>
>> NUS
>>
>>
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>
> --
> =======================================================================
> Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
>   Center for Molecular Modeling   --   University of Pennsylvania
> Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
> tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
> =======================================================================
> If you make something idiot-proof, the universe creates a better idiot.
>
>
>
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-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.