Pseudo hard-sphere potential for use in continuous molecular-dynamics simulation of spherical and chain molecules

Jover, Julio F.; Haslam, Andrew J.; Galindo, Amparo; Jackson, George; Müller, Erich A.

doi:10.1063/1.4754275

Cited by 112 publications

(140 citation statements)

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“…The bead-bead interactions are described with a soft-repulsive potential based on the Lennard-Jones (LJ) potential truncated and shifted to zero at the cut-off distance r c = 2 1/6 σ . This potential is commonly referred to as the Weeks-Chandler-Andersen (WCA) potential [84,85]. Particles are placed in a rectan-…”

Section: Molecular Model and Simulation Detailsmentioning

confidence: 99%

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

2018

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We study the structure and liquid-crystalline phase behaviour of a model of confined non-convex circular soft-repulsive nanorings in a planar slit geometry using molecular-dynamics simulation. The separation distance between the structureless parallel soft-repulsive walls is made large enough to allow for the formation of a distinct bulk phase in the central region of the box which is in coexistence with the adsorbed fluid thus allowing the analysis of single-wall effects. As the density of the particles is increased, the fluid adsorbs (wets) onto the planar surfaces leading to the formation of well-defined smectic-A layers with a spacing proportional to the diameter of the rings. An analysis of the nematic order parameter at distances perpendicular to the surface reveals that the particles in each layer exhibit anti-nematic behaviour and planar (edge-on) anchoring relative to the short symmetry axis of the rings. This behaviour is in stark contrast to the behaviour observed in convex disc-like particles that have the tendency to form nematic (discotic) structures with homeotropic (face-on) anchoring. The smectic phases formed by nanorings in the bulk and under confinement are characterised by the formation of low-density layered liquid-crystalline states with large voids, referred to here as lacuna smectic phases. In contrast to what is typically found for confined liquidcrystalline systems involving convex particles, no apparent biaxiality is found for nanorings in planar confinement. We argue that formation of the low-density lacuna smectic layers with planar anchoring is a consequence of the non-convex shape of the circular rings that allow for interpenetration between the particles as observed for nanorings under bulk conditions [C. Avendaño, G.

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Section: Molecular Model and Simulation Detailsmentioning

confidence: 99%

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

2018

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“…Unlike the true HS potential, this interaction is not athermal and one is required to set a temperature. It has been previously shown [106] that an excellent representation of (athermal) HS systems is provided at a reduced temperature of T * = k B T/ = 1.5, where k B is the Boltzmann constant and T the absolute temperature. At this condition, the size parameter, σ , effectively matches the HS diameter, i.e., no density correction is required.…”

Section: Athermal Mixture Of Hard Spheres and Tangent Hard-sphere Chainsmentioning

confidence: 99%

“…The phase behaviour of the colloid-polymer system is examined both using the Wertheim TPT1 relations and direct molecular simulation. In our simulations the (discontinuous) HS interaction is modelled using a (continuous) pseudo-hard-sphere (PHS) potential [106]. This approach has the advantage that it allows straightforward and efficient simulation using 'off-the-shelf ' MD software, and the deployment of parallel computation with no loss of accuracy.…”

Section: Athermal Mixture Of Hard Spheres and Tangent Hard-sphere Chainsmentioning

confidence: 99%

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Fluid–fluid coexistence in an athermal colloid–polymer mixture: thermodynamic perturbation theory and continuum molecular-dynamics simulation

et al. 2015

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Using both theory and continuum simulation, we examine a system comprising a mixture of polymer chains formed from 100 hard-sphere (HS) segments and HS colloids with a diameter which is 20 times that of the polymer segments. According to Wertheim's first-order thermodynamic perturbation theory (TPT1) this athermal system is expected to phase separate into a colloid-rich and a polymer-rich phase. Using a previously developed continuous pseudo-HS potential [J. F. Jover, A. J. Haslam, A. Galindo, G. Jackson, and E. A. Muller, J. Chem. Phys. 137, 144505 (2012)], we simulate the system at a phase point indicated by the theory to be well within the two-phase binodal region. Molecular-dynamics simulations are performed from starting configurations corresponding to completely phase-separated and completely pre-mixed colloids and polymers. Clear evidence is seen of the stabilisation of two coexisting fluid phases in both cases. An analysis of the interfacial tension of the phase-separated regions is made; ultra-low tensions are observed in line with previous values determined with square-gradient theory and experiment for colloid-polymer systems. Further simulations are carried out to examine the nature of these coexisting phases, taking as input the densities and compositions calculated using TPT1 (and corresponding to the peaks in the probability distribution of the density profiles obtained in the simulations). The polymer chains are seen to be fully penetrable by other polymers. By contrast, from the point of view of the colloids, the polymers behave (on average) as almost-impenetrable spheres. It is demonstrated that, while the average interaction between the polymer molecules in the polymer-rich phase is (as expected) soft-repulsive in nature, the corresponding interaction in the colloid-rich phase is of an entirely different form, characterised by a region of effective intermolecular attraction.

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“…In order to avoid problems associated with impulsive forces due to hard sphere interactions, we adopted a smooth repulsive potential developed by Jover and co-workers 25 , The so-called Mie potential is given by,…”

Section: Molecular Dynamics Simulation Detailsmentioning

confidence: 99%

Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids

Nordholm

et al. 2016

The Journal of Chemical Physics

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. (2016). Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids. Journal of Chemical Physics, 145(23), [234510]. https://doi.org/10.1063/1.4972214General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Ion Pairing and Phase Behaviour of an Asymmetric Restricted Primitive Model of Ionic LiquidsHongduo Lu †1 , Bin Li †1 , Sture Nordholm 2 , Clifford E. Woodward 3 , and Jan formed from ion pairs. The present exploration of the system focuses on the ion pair formation mechanism, the relative concentration of paired and free ions and the consequences for the cohesive energy, and the tendency to form fluid or solid phase. In contrast to studies of similar (though not identical) models in the past, we focus on behaviours at room temperature. By MC and MD simulations of such systems composed of monovalent ions of hard-sphere (or * To whom correspondence should be addressed 1 essentially hard-sphere) diameter equal to 5 Å and a charge displacement from hard-sphere origin ranging from 0 to 2 Å we find that ion pairing dominates for b larger than 1 Å. When b exceeds about 1.5 Å, the system is essentially a liquid of dipolar ion pairs, with a small presence of free ions. We also investigate dielectric behaviours of corresponding liquids, composed of purely dipolar species. Many basic features of ionic liquids appear to be remarkably consistent with those of our ARPM at ambient conditions, when b is around 1 Å. However, the rate of self-diffusion and, to a lesser extent, conductivity are overestimated, presumably due to the simple spherical shape of our ions in the ARPM. The relative simplicity of our ARPM in relation to the rich variety of new mechanisms and properties it introduces, and to the numerical simplicity of its exploration by theory or simulation, makes it an essential step on the way towards representation of the full complexity of ionic liquids.

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Pseudo hard-sphere potential for use in continuous molecular-dynamics simulation of spherical and chain molecules

Cited by 112 publications

References 110 publications

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

Fluid–fluid coexistence in an athermal colloid–polymer mixture: thermodynamic perturbation theory and continuum molecular-dynamics simulation

Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids

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