COPSS (Continuum--Particle Simulation Software) augments standard molecular dynamics and Monte-Carlo codes, permitting particle--field coupling. COPSS presents not only a set of methods, but also aims to provide a unified, extensible framework adaptable to generic molecular simulations.

COPSS is open-source and distributed under the GNU General Public License. It is developed at Argonne National Laboratory and the University of Chicago.

Seamless Integration

COPSS is designed from the ground up to connect to arbitrary molecular simulation codes through minimal programming effort. It targets specific interoperability with open-source codes such as GROMACS and LAMMPS, and is constantly growing to incorporate other open-source, proprietary, and bespoke codes.

What does it do?

The continuum--particle coupling provided by COPSS enables the spanning of multiple timescales in simulation. The initial suite of routines is built around the General-geometry Ewald-like Method (GgEM) which enables simulations such as that shown below, where a discrete polymer chain, representing DNA, is embedded in a background solvent, and confined to a nanoscopic channel; without coupling algorithms such as GgEM, such simulations are impossible.

The continuum--particle coupling of COPSS permits efficient simulation of many-body systems such as the DNA nanoslit (see video) on the timescales of polymer diffusion. In the first video, 84 kilobase DNA is simulated under confinement in a nanochannel with full hydrodynamic coupling to itself and the system boundaries.

COPSS also permits the simulation of electrostatic interactions with polarization effects in heterogeneous dielectric media in an accurate, highly efficient manner. In the second video, 10 polarizable micron-sized particles are simulated in an vacuum environment where only long-range electrostatic interaction and short-range excluded volume interaction affect their motion. The electrostatic forces are calculated by COPSS at each time step, and the particles' positions are evolved by coupling COPSS with LAMMPS.