CCL: Question regarding availability of a simulation code

 Sent to CCL by: Josh BERRYMAN [Josh.Berryman]-[]
 The normal definition of hard spheres is as an infinite potential stepping
 instantly down to zero at r=.5.  That is not compatible with defining forces
 usefully, so HS simulations are done with event-driven MD rather than the normal
 fixed-timestep methods.  Marcus Bannerman et al.'s DynamO is an open-source
 event-driven HS code.
 The best mixing of ED simulations with a continuous potential such as the
 Coulomb force is not obvious.  One approach is to discretise the Coulomb
 potential, and treat level crossings as a special type of collision.  Another
 approach might be to run fixed-timestep MD with EDMD taking place in between the
 fixed timesteps.
 For lengthscales where the HS potential is meaningful (micrometres and up) you
 might find that you are in low Reynolds-number-land, in which case it is
 probably quite OK to use a Brownian Dynamics approximation: you can evolve the
 system using Monte Carlo in this case, with small fixed-size steps in space,
 thus avoiding the need to define forces.  Code for this approach is extremely
 simple, most groups just write their own see eg. Frenkel & Smit's book, or
 Allen & Tildesley, both of which have code recipies.  Allen & Tildesley
 is free online as far as I can remember.
 > From:
 [] on behalf of Susi Lehtola
 susi.lehtolaa/ [owner-chemistry(0)]
 Sent: Sunday, November 08, 2015 05:06 PM
 Subject: CCL: Question regarding availability of a simulation code
 Sent to CCL by: Susi Lehtola [susi.lehtola\a/]
 On 11/06/2015 10:04 PM, Rakesh Srivastava wrote:
 > Dear scholars,
 > I want to know, is there any MD code available which can simulate a
 > system of spherical particles which interact via hard sphere and
 > electrostatic potential.
 > Thanks in advance.
 For instance GROMACS ( can do this, you'd just
 probably have to use a tabulated potential for your calculation. There
 was some discussion on the mailing list a few years ago
 Mr. Susi Lehtola, PhD             Chemist Postdoctoral Fellow
 susi.lehtola+/   Lawrence Berkeley National Laboratory  USA