|
From: | Georg Rempfer |
Subject: | Re: [ESPResSo-users] Espressomd-users Digest, Vol 83, Issue 4 |
Date: | Thu, 21 Sep 2017 10:03:03 +0200 |
Hello everyone!Am I making any mistake assuming that the mass of each particle in Espresso is inherently fixed irrespective of the size of the particles. The gamma should be size-dependent instead.On Wed, Sep 20, 2017 at 5:00 PM, <espressomd-users-request@nongnu.org > wrote:Send Espressomd-users mailing list submissions to
address@hidden
To subscribe or unsubscribe via the World Wide Web, visit
https://lists.nongnu.org/mailman/listinfo/espressomd-users
or, via email, send a message with subject or body 'help' to
address@hiddenu.org
You can reach the person managing the list at
address@hiddenorg
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Espressomd-users digest..."
Today's Topics:
1. Re: Choice of timestep and langevin-gamma (Georg Rempfer)
2. Re: Choice of timestep and langevin-gamma
(address@hidden)
------------------------------------------------------------ ----------
Message: 1
Date: Tue, 19 Sep 2017 21:42:44 +0200
From: Georg Rempfer <address@hidden>
To: "address@hidden" <address@hidden>
Subject: Re: [ESPResSo-users] Choice of timestep and langevin-gamma
Message-ID:
<CAA6P0aKkgh15M8Dr_z0vh75mrsEWaddress@hidden >gmail.com
Content-Type: text/plain; charset="utf-8"
There is a feature called LANGEVIN_PER_PARTICLE, that allows you to set
different gammas for different particles.
On Tue, Sep 19, 2017 at 4:38 PM, Clemens Jochum <address@hidden
> wrote:
> Dear all,
>
> I just noticed a mistakeI made. In the user-guide it is stated that
> gamma is not the inverse relaxation time tau anymore, but it is now
> defined as mass / tau. In this case if I want to achieve tau^-1 = 1.5
> ps^-1 for a particle of mass2 = 660, I have to set gamma = 100, which
> seems high.
>
> At the same time the other particles with mass1 = 20 will have tau^-1 =
> 50 ps^-1 (mass2 / mass1 = 33). But with the way the Langevin-thermostat
> is implemented in ESPResSo it is not possible to prevent this large
> difference between the two particle types with different masses.
>
> Could this lead to some problems? Or is there a way to assign a fixed
> value to tau and tau^-1 for all masses in ESPResSo?
>
> Best,
> Clemens
>
> > The other parameter I am concerned about is gamma of the
> > langevin-thermostat. So far I just used gamma = 1. = 10 ps^-1, which as
> > I recently read is a little bit high. In my system I simulate a charged
> > macromolecule with counter-ions in an implicit solvent (water). Is a
> > value of gamma = 0.2 = 2 ps^-1 a good fit?
>
>
> On 19.09.2017 13:11, Clemens Jochum wrote:
> > Dear all,
> >
> > I read previously that for a system with Temp = 1. and mass = 1. a good
> > value for the timestep is 0.01. I have Temp = 2.5 and mass1 = 20 and
> > mass2 = 660. Is it correct to assume that I can scale the timestep
> > inversely to the thermal velocity with a factor of (m / kT)^(1/2) ~ 3
> > (using the mass1)? I have been using a timestep of 0.05 = 5e-15 s so far
> > without any major problems.
> >
> > The other parameter I am concerned about is gamma of the
> > langevin-thermostat. So far I just used gamma = 1. = 10 ps^-1, which as
> > I recently read is a little bit high. In my system I simulate a charged
> > macromolecule with counter-ions in an implicit solvent (water). Is a
> > value of gamma = 0.2 = 2 ps^-1 a good fit?
> >
> > Best,
> > Clemens
> >
> >
> >
> >
> >
> >
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.nongnu.org/archive/html/espressomd-users/attac >hments/20170919/76acc735/attac hment.html
------------------------------
Message: 2
Date: Tue, 19 Sep 2017 23:16:51 +0200
From: "address@hidden" <address@hidden>
To: <address@hidden>
Subject: Re: [ESPResSo-users] Choice of timestep and langevin-gamma
Message-ID: <afb63af5-1462-9ef7-a585-2aab2address@hidden >
Content-Type: text/plain; charset="utf-8"; format=flowed
Thanks! That looks like what I need.
Best,
Clemens
On 09/19/2017 09:42 PM, Georg Rempfer wrote:
> There is a feature called LANGEVIN_PER_PARTICLE, that allows you to set
> different gammas for different particles.
>
> On Tue, Sep 19, 2017 at 4:38 PM, Clemens Jochum
> <address@hidden <mailto:address@hiddenac.at >> wrote:
>
> Dear all,
>
> I just noticed a mistakeI made. In the user-guide it is stated that
> gamma is not the inverse relaxation time tau anymore, but it is now
> defined as mass / tau. In this case if I want to achieve tau^-1 = 1.5
> ps^-1 for a particle of mass2 = 660, I have to set gamma = 100, which
> seems high.
>
> At the same time the other particles with mass1 = 20 will have tau^-1 =
> 50 ps^-1 (mass2 / mass1 = 33). But with the way the Langevin-thermostat
> is implemented in ESPResSo it is not possible to prevent this large
> difference between the two particle types with different masses.
>
> Could this lead to some problems? Or is there a way to assign a fixed
> value to tau and tau^-1 for all masses in ESPResSo?
>
> Best,
> Clemens
>
> > The other parameter I am concerned about is gamma of the
> > langevin-thermostat. So far I just used gamma = 1. = 10 ps^-1, which as
> > I recently read is a little bit high. In my system I simulate a charged
> > macromolecule with counter-ions in an implicit solvent (water). Is a
> > value of gamma = 0.2 = 2 ps^-1 a good fit?
>
>
> On 19.09.2017 13:11, Clemens Jochum wrote:
> > Dear all,
> >
> > I read previously that for a system with Temp = 1. and mass = 1. a
> good
> > value for the timestep is 0.01. I have Temp = 2.5 and mass1 = 20 and
> > mass2 = 660. Is it correct to assume that I can scale the timestep
> > inversely to the thermal velocity with a factor of (m / kT)^(1/2) ~ 3
> > (using the mass1)? I have been using a timestep of 0.05 = 5e-15 s
> so far
> > without any major problems.
> >
> > The other parameter I am concerned about is gamma of the
> > langevin-thermostat. So far I just used gamma = 1. = 10 ps^-1,
> which as
> > I recently read is a little bit high. In my system I simulate a
> charged
> > macromolecule with counter-ions in an implicit solvent (water). Is a
> > value of gamma = 0.2 = 2 ps^-1 a good fit?
> >
> > Best,
> > Clemens
> >
> >
> >
> >
> >
> >
>
>
>
>
------------------------------
Subject: Digest Footer
_______________________________________________
Espressomd-users mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/espressomd-users
------------------------------
End of Espressomd-users Digest, Vol 83, Issue 4
***********************************************
[Prev in Thread] | Current Thread | [Next in Thread] |