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Re: [ESPResSo-users] Question about the setting of agrid in L-B fluidics

From: Joe Ada
Subject: Re: [ESPResSo-users] Question about the setting of agrid in L-B fluidics
Date: Tue, 12 May 2015 09:53:00 -0400

Thanks Peter. I believe with LB fluid, a 16um long polymer with 50nm persistance length is even hopeless.

I thought if I started with generating them in a SAW way, I may reach the equilibrium status reasonably fast with the help of gpu p3m. 

So could I know the practical max number of beads people have done for time up to 100ms using gpu system with LB fluid? 


On Mon, May 11, 2015 at 11:43 AM, Georg Rempfer <address@hidden> wrote:
We have had a similar question recently:

"simulating 4k long polymer with Langevin dynamics is hopeless. The dynamics of such a long chain is far too slow to obtain meaningful statistics in a reasonable time (human lifetime). The characteristic time scale increases roughly as N^{5/3}. If you need such long chains, you should use MC."
    - Peter Košovan 

On Mon, May 11, 2015 at 5:22 PM, Joe Ada <address@hidden> wrote:

I try to run a model with ions and polyelectrolyte in solution in external electric field. The polymer is a 20um long chain with 1600 beads and springs, and the total number of the coions and counterions are 3*1600. What I care about is the hydrodynamic interaction between different beads, beads-ions and ions from the LB part. 

What is the practical setting of this grid number? 

My understanding of the agrid is that it determines the spacial resolution of the fluid. In the user guide, it says "It should also be noted that the LB nodes are located at 0.5, 1.5, 2.5, etc (in terms of agrid).". May I assume the resolution is 0.5 agrid? Does that mean that I have to make this 0.5 *agrid smaller than the typical distance ion travels during time tau*MD time step? 


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