What is Dissipative Particle Dynamics:

One of the current theoretical challenges is to understand the basic principles that govern collective properties of soft--matter systems. From a modeling point of view, these systems are problematic due to the fact that numerous phenomena take place at mesoscopic time and length scales, while the most accurate ``brute--force'' molecular dynamics simulations are limited to microscopic time and length scales. To overcome this problem, a number of ``coarse--grained'' approaches have been suggested and developed to simplify the underlying microscopic model while retaining the essential physics.

In 1992 Hoogerbrugge and Koelman introduced a new coarse-grained method for fluid dynamics simulation coined Dissipative Particle Dynamics (DPD). From a technical point of view, DPD differs from Molecular Dynamics (MD) in two respects:

1. The conservative pairwise forces between DPD particles (which represent clusters of microscopic particles) are soft--repulsive, which makes it possible to extend the simulations to longer time scales.
2. Second, a special ``DPD thermostat'' for the canonical ensemble is implemented in terms of dissipative as well as random pairwise forces such that the momentum is locally conserved, which results in the emergence of hydrodynamic flow effects on the macroscopic scale.

DPD Simulation of liposome formation:

• Below are snapshots of a DPD simulation of liposome formation (Nikunen, Karttunen & Vattulainen). The second row shows a cross-section of the system. Water has been removed for clarity.

• The system has roughly 86000 particles.

Movies of liposome formation:

• A small MPEG movie (balls and springs) of liposome formation
• The same as above but the looking at a cross section of the liposome. One molecule is tagged.
• Here is a large (40MB) mpeg movie (sticks) of the process. Red denotes the head group and and gray the tail: MPEG movie of liposome formation
• Note: Water (about 80000) is removed from the above movies for clarity.

Movies of DPD simulations of block copolymers:

• Simulation of A3B7 block copolymer melt. (7.1 MB)
• Simulation of A3B7 block copolymer melt but only the A part shown. (10.5 MB)
  

• Coarse-Grained Model for Phospholipid/Cholesterol Bilayer
  Teemu Murtola, Emma Falck, Michael Patra, Mikko Karttunen, Ilpo Vattulainen
  J. Chem. Phys.121 9156-9165 (2004).
  [cond-mat/0406764]     [online]
  Selected for the November 1, 2004 issue of the Virtual Journal of Biological Physics Research

• How would you integrate the equations of motion in dissipative particle dynamics simulations?
  Petri Nikunen, Mikko Karttunen, and Ilpo Vattulainen
  Comp. Phys. Comm. 153, 407-421 (2003)
  [Online] [Preprint]

• On coarse-graining by the inverse Monte Carlo method: Dissipative Particle Dynamics simulations made to a precise tool in soft matter modeling,
  Alexander P. Lyubartsev, Mikko Karttunen, Ilpo Vattulainen, and Aatto Laaksonen
  Soft Materials 1, 121-137 (2002).
  [Online] [Preprint]

• Integration schemes for dissipative particle dynamics simulations: From softly interacting systems towards hybrid models, Ilpo Vattulainen, Mikko Karttunen, Gerhard Besold, and James Polson, J. Chem. Phys., 116, pp. 3967-3979 (2002)
  [ Online] [preprint]

• Towards better integrators for dissipative particle dynamics simulations, Gerhard Besold, Ilpo Vattulainen, Mikko Karttunen, and James M. Polson, Phys. Rev. E, vol. 63, pp. R7611-R7614 (2000)
  [Online] [preprint]

• See our publication list.

General references:

• Robert D. Groot and Patrick B. Warren, "Dissipative particle dynamics: Bridging the gap between atomistic and mesoscopic simulation", J. Chem. Phys. 107/11 (1997) 4423-4435
• Patrick B. Warren, "Dissipative particle dynamics", Current Opinion in Colloid & Interface Science 3/6 (1998) 620-624