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Re: [ESPResSo-users] Doubt regarding self propulsion and diamond lattice

From: Nairhita Samanta
Subject: Re: [ESPResSo-users] Doubt regarding self propulsion and diamond lattice
Date: Fri, 28 Oct 2016 15:27:14 +0530

Hi Joost!

Thank you very much. I have seen this paper before actually. I am not doing LB simulations. I wanted to know if one uses Langevin thermostat without using any quaternion if the tip of the triangle is placed towards positive z axis, then if due to thermal fluctuation that particular tip now points towards positive x axis, then the triangle now can move towards positive x or negative x if one can neglect the effect of thermal fluctuation for the moment (using the present algorithm of Espresso)?

If I now want the particle to move only towards the tip or base I need to use quaternion?


On Fri, Oct 28, 2016 at 2:56 PM, Joost de Graaf <address@hidden> wrote:
Hello Nairhita,

Asymmetric particles are way more tricky than symmetric ones, I would strongly advise you to use the algorithm with caution and really think carefully about what you want to achieve. However, I am not sure what you mean by asymmetric here, or at least not what level of asymmetry you want to achieve. We have used the algorithm before to study triangles

This works well. However, something like an L-shape, which would follow a circular trajectory, will require much more thought and modification of either the algorithm (in the case of a Langevin thermostat), or clever use of building blocks with motors and non-self-propelled bits using the virtual sites. In the case of the LB simulations, I'm not presently sure how to best go about this, and I would advise you not to use the method to study that kind of shapes, although something with a mirror symmetry plane (triangle, rod, or cone) would be fine.

You can have the particle move both towards the tip and the base of the triangle, as you can see in the paper, but this requires you to properly set up the quaternion for the direction of motion, relative to the shape of your asymmetric object. Just give it a try and visualize your result, it should become really clear what the algorithm does from just looking at a few movies of the simulations. I hope this helps.

Best Wishes,


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