Langevin references
Matthias Krack
matthia... at psi.ch
Thu Mar 19 09:11:46 UTC 2009
You are right, Ondrej.
The input parameter shadow_gamma is not needed for the setup of the
scheme detailed in the Kuhne paper.
It could be useful for some testing purposes, but I have never used
it, yet.
Matthias
On Mar 19, 9:50 am, Ondrej Marsalek <ondrej.... at gmail.com> wrote:
> Hi,
>
> this is not what I understood from the papers, the message on this
> mailing list from Matthias or from the source code, therefore please
> correct me if I am wrong in the following.
>
> Gamma and noisy_gamma get used for the generation of the white noise,
> as seen from this source line:
>
> simpar_methods.F:83: simpar%var_w =
> 2.0_dp*simpar%temp_ext*simpar%dt*(simpar%gamma+simpar%noisy_gamma)
>
> which corresponds to the RHS in [Kuhne2007].
>
> Shadow_gamma, on the other hand, seems to be added to the Langevin
> gamma only for dissipation, as illustrated by the line
>
> integrator.F:164: gam = simpar%gamma+simpar%shadow_gamma
>
> because the variable gam is the one later used in the propagator. It
> is not clear to me what is the intended purpose of shadow_gamma, but
> it looks like it could be used to introduce artificial drag into the
> system, for example for the purpose of testing the whole procedure of
> propagation with noisy forces.
>
> Is this correct or am I reading the code incorrectly?
>
> Best,
> Ondrej
>
> On Wed, Mar 18, 2009 at 15:54, Fawzi Mohamed <fa... at gmx.ch> wrote:
>
> > On 18-mar-09, at 15:50, Daniel_M wrote:
>
> >> Hi all,
>
> >> I am doing some MD calculations employing the Langevin Dynamics and I
> >> don't know what is exactly the role of the parameter SHADOW_GAMMA. I
> >> have been reading the ref. [Kuhne2007] but I understand that in this
> >> ref. only the GAMMA and NOISY_GAMMA are mentioned (as gamma_L and
> >> gamma_D respectively). Could anybody give me some more references
> >> about this?
>
> > Shadow gamma is the dissipation that the approximate propagation
> > introduces
> > You have to evaluate it by doing a test run.
>
> > If you are interested in doing a normal langevin dynamics then you
> > don't need shadow_gamma.
>
> > Fawzi
>
> >> Thanks a lot!
>
> >> Daniel
>
>
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