Rosalind J Allen

Publications (2)5.64 Total impact

• Article: Osmosis in a minimal model system.

  Thomas W Lion, Rosalind J Allen
  [show abstract] [hide abstract]
  ABSTRACT: Osmosis is one of the most important physical phenomena in living and soft matter systems. While the thermodynamics of osmosis is well understood, the underlying microscopic dynamical mechanisms remain the subject of discussion. Unravelling these mechanisms is a prerequisite for understanding osmosis in non-equilibrium systems. Here, we investigate the microscopic basis of osmosis, in a system at equilibrium, using molecular dynamics simulations of a minimal model in which repulsive solute and solvent particles differ only in their interactions with an external potential. For this system, we can derive a simple virial-like relation for the osmotic pressure. Our simulations support an intuitive picture in which the solvent concentration gradient, at osmotic equilibrium, arises from the balance between an outward force, caused by the increased total density in the solution, and an inward diffusive flux caused by the decreased solvent density in the solution. While more complex effects may occur in other osmotic systems, our results suggest that they are not required for a minimal picture of the dynamic mechanisms underlying osmosis.
  The Journal of chemical physics 12/2012; 137(24):244911. · 3.09 Impact Factor
• Source

  Available from: ArXiv

  Article: Computing the local pressure in molecular dynamics simulations.

  Thomas W Lion, Rosalind J Allen
  [show abstract] [hide abstract]
  ABSTRACT: Computer simulations of inhomogeneous soft matter systems often require accurate methods for computing the local pressure. We present a simple derivation, based on the virial relation, of two equivalent expressions for the local (atomistic) pressure in a molecular dynamics simulation. One of these expressions, previously derived by other authors via a different route, involves summation over interactions between particles within the region of interest; the other involves summation over interactions across the boundary of the region of interest. We illustrate our derivation using simulations of a simple osmotic system; both expressions produce accurate results even when the region of interest over which the pressure is measured is very small.
  Journal of Physics Condensed Matter 07/2012; 24(28):284133. · 2.55 Impact Factor