Comparison of dissipative particle dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

Abstract

In this work we compare and characterize the behavior of Langevin and Dissipative Particle Dynamics (DPD) thermostats in a broad range of non-equilibrium simulations of polymeric systems. Polymer brushes in relative sliding motion, polymeric liquids in Poiseuille and Couette flows, and brush-melt interfaces are used as model systems to analyze the efficiency and limitations of different Langevin and DPD thermostat implementations. Widely used coarse-grained bead-spring models under good and poor solvent conditions are employed to assess the effects of the thermostats. We considered equilibrium, transient, and steady state examples for testing the ability of the thermostats to maintain constant temperature and to reproduce the underlying physical phenomena in non-equilibrium situations. The common practice of switching-off the Langevin thermostat in the flow direction is also critically revisited. The efficiency of different weight functions for the DPD thermostat is quantitatively analyzed as a function of the solvent quality and the non-equilibrium situation.

Multiscale modeling of emergent materials: biological and soft matter

“…160 We are also not limited to soft single parameter intermolecular forces or uniform particle mass and force cutoff as the DPD thermostat has been used outside of this context. 161 Intra-molecular forces other than harmonic ''springs'' have been implemented including 2-4 interactions, 140 FENE springs 161 and the accuracy of the surfactant simulation has been increased by Shillcock et al 155 through the addition of a three body potential acting between consecutive bead triples. We are finally not limited to the thermostating being provided by dissipative and random forces, as the now widely used Lowe-Andersen themostat 162 and the extension of this method proposed by Stoyanov and Groot 163 attest.…”

Water flow in carbon nanotubes: The effect of tube flexibility and thermostat

“…All the thermostats considered in our study are widely used in molecular simulations, but they are not suitable to fully account for the system hydrodynamics, when subjected to an external force. 50,51 However, the drawback of the Langevin thermostat, in comparison to the Nosé-Hoover and Berendsen thermostats, is that the frictional and random forces of the Langevin thermostat can damp the system dynamics, thus reducing the flow velocity in nonequilibrium simulations. In fact, the forces exerted by fluid onto the walls were highest in systems coupled to the Langevin thermostat, i.e., the interfacial friction has been increased considerably.…”

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

“…The parameter γ was set to unity in all simulations, because this value allows to maintain constant temperature and doesn't produce a significative over-damping of conservative forces [55]. The random variable η ij has zero mean and second moment η ij (t)η kl (t ′ ) = δ ik δ jl δ(t − t ′ ).…”

“…The random variable η ij has zero mean and second moment η ij (t)η kl (t ′ ) = δ ik δ jl δ(t − t ′ ). The usual choice of the weight functions for continuous forces was made [53,55].…”

“…We used the dissipative particle dynamics (DPD) scheme [50,51] to perform the simulations at constant temperature. An important feature of this thermostat is that it accounts for correct hydrodynamic behaviour [52], which is essential to obtain reliable results out of equilibrium [53][54][55]. The equation of motion for a particle reads:…”