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Re: [ESPResSo-users] Help Active system

From: Nairhita Samanta
Subject: Re: [ESPResSo-users] Help Active system
Date: Fri, 30 Dec 2016 10:56:32 +0530

Dear Joost,

Thank you very much for your reply. I want to apologize for sending the same mail repeatedly, as due to some reason my mails were not getting delivered initially.

I wanted to clarify that from your mail, I understood that the system with active particles will work fine even if the ROTATIONAL_INERTIA feature is not switched on. The ENGINE itself takes care of rotation and rotational inertia.

Although I have already performed some simulations with ENGINE and ROTATION features on but not the ROTATIONAL_INERTIA as I did not know about this. However, I have not provided any separate gamma_rot value, so I assume it considers gamma_rot=gamma_trans.

I understand need to be more careful while choosing the value for swimming velocity and diffusion coefficient.

Thanking you.


On Fri, Dec 30, 2016 at 3:10 AM, Joost de Graaf <address@hidden> wrote:
Dear Nairhita,

It would appear that you sent the same message several times, so I'll only reply to this one.

The ENGINE feature implies other features, such as ROTATION. If you compile in ROTATIONAL_INERTIA but do not set it, ESPResSo will use the default values. Choosing a different value will modify the physics, but if you don't specify it, it will be as though you did not activate the feature. Obviously, everything that can rotate in MD has rotational inertia.

Also, please be mindful that high values of the swimming velocity (force) need to be paired with appropriately chosen friction coefficients and length of the time step, to be in the regime where the integrator is stable and produces the right physics.

Best Wishes,


On 29 December 2016 at 14:55, Nairhita Samanta <address@hidden> wrote:
Hello all!

I want to work on a active system. I understood I need "ENGINE" feature on in the myconfig.hpp file for particle to swim. However do I need the "ROTATION" and "ROTATIONAL INERTIA" features as well in myconfig.hpp?

What does the "ROTATIONAL INERTIA" do? In a Active Matter tutorial by Joost de Graaf and Henri Menke I found it has been suggested to activate this also. What if I have just "ENGINE"and "ROTATION" features on and not "ROTATIONAL INERTIA" for a value of v_swim=10. Does it somehow affects the physics?

Or "ROTATIONAL INERTIA" is just required if one wants anisotropic rotational diffusion?


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