Papers by Nigel B Wilding
A simulation technique is described for quantifying the contribution of three-body interactions t... more A simulation technique is described for quantifying the contribution of three-body interactions to the thermodynamical properties of coarse-grained representations of complex fluids. The method is based on comparing the third virial coefficient B3 for a complex fluid with that of an approximate coarse-grained model described by a pair potential. To obtain B3 we introduce a new technique which expresses its value in terms of the measured volume-dependent asymptote of a certain structural function. The strategy is applicable to both Molecular Dynamics and Monte Carlo simulation. Its utility is illustrated via measurements of three-body effects in models of star polymer and highly size-asymmetrical colloid-polymer mixtures. arXiv:1403.3368v2 [cond-mat.soft]
We report experimental and simulation studies of the structure of a monolayer of indented (&a... more We report experimental and simulation studies of the structure of a monolayer of indented ("lock and key") colloids, on a planar surface. On adding a non-absorbing polymer with prescribed radius and volume fraction, depletion interactions are induced between the colloids, with controlled range and strength. For spherical particles, this leads to crystallisation, but the indented colloids crystallise less easily than spheres, in both simulation and experiment. Nevertheless, simulations show that indented colloids do form plastic (rotator) crystals. We discuss the conditions under which this occurs, and the possibilities of lower-symmetry crystal states. We also comment on the kinetic accessibility of these states.
Lecture Notes in Physics, 2002
We identify the origin, and elucidate the character of the extended time-scales that plague compu... more We identify the origin, and elucidate the character of the extended time-scales that plague computer simulation studies of first and second order phase transitions. A brief survey is provided of a number of new and existing techniques that attempt to circumvent these problems. Attention is then focused on two novel methods with which we have particular experience: “Wang-Landau sampling” and
Physical Review E, 1997
We consider the liquid-gas phase boundary in a binary fluid mixture near its critical end point. ... more We consider the liquid-gas phase boundary in a binary fluid mixture near its critical end point. Using general scaling arguments we show that the diameter of the liquid-gas coexistence curve exhibits singular behaviour as the critical end point is approached. This prediction is tested by means of extensive Monte-Carlo simulations of a symmetrical Lennard-Jones binary mixture within the grand canonical ensemble. The simulation results show clear evidence for the proposed singularity, as well as confirming a previously predicted singularity in the coexistence chemical potential Upton, Phys. Rev. Lett. 65, 2402 (1990)]. The results suggest that the observed singularities, particularly that in the coexistence diameter, should also be detectable experimentally.
Annual Reviews of Computational Physics IV, 1996
Physical Review E, 1998
A solid substrate, when exposed to a vapour, can interact with it in such a way that sufficiently... more A solid substrate, when exposed to a vapour, can interact with it in such a way that sufficiently close to liquid-vapour coexistence a macroscopically thick liquid wetting layer is formed on the substrate surface. If such a wetting transition occurs for a binary fluid mixture in the vicinity of the critical end point of demixing transitions, critical fluctuations lead to additional longranged interactions (Casimir forces) within the wetting layer, changing its equilibrium thickness. We demonstrate this effect by Monte-Carlo simulations of wetting layers of a symmetrical Lennard-Jones binary fluid mixture near its critical end point. The results suggest that the effect should also be detectable in corresponding wetting experiments.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
We describe a general simulation scheme for assessing the thermodynamic consequences of neglectin... more We describe a general simulation scheme for assessing the thermodynamic consequences of neglecting many-body effects in coarse-grained models of complex fluids. The method exploits the fact that the asymptote of a simple-to-measure structural function provides direct estimates of virial coefficients. Comparing the virial coefficients of an atomistically detailed system with those of a coarse-grained version described by pair potentials, permits the role of many-body effects to be quantified. The approach is applied to two models: (i) a size-asymmetrical colloid-polymer mixture, and (ii) a solution of star polymers. In the latter case, coarse-graining to an effective fluid described by pair potentials is found to neglect important aspects of the true behavior.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
We report a Monte Carlo finite-size scaling study of the demixing transition of a symmetrical Len... more We report a Monte Carlo finite-size scaling study of the demixing transition of a symmetrical Lennard-Jones binary fluid mixture. For equal concentration of species, and for a choice of the unlike-to-like interaction ratio delta=0.7, this transition is found to be continuous at liquid-vapor coexistence. The associated critical end point exhibits an Ising-like universality. These findings confirm those of earlier smaller scale simulation studies of the same model, but contradict the findings of recent integral equation and hierarchical reference theory investigations.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2002
We report extensive simulation studies of phase behavior in single component systems of particles... more We report extensive simulation studies of phase behavior in single component systems of particles interacting via a core-softened interparticle potential. Two recently proposed examples of such potentials are considered; one in which the hard core exhibits a shoulder [Sadr-Lahijany et al., Phys. Rev. Lett. 81, 4895 (1998)], and the other in which the softening takes the form of a linear ramp [Jagla, Phys. Rev. E 63, 061501 (2001)]. Using a combination of state-of-the-art Monte Carlo methods, we obtain the gas, liquid, and solid phase behavior of the shoulder model in two dimensions. We then focus on the thermodynamic anomalies of the liquid phase, namely, maxima in the density and compressibility as a function of temperature. Analysis of the finite-size behavior of these maxima suggests that, rather than stemming from a metastable liquid-liquid critical point, as previously supposed, they are actually induced by the quasicontinuous nature of the two dimensional freezing transition. ...
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1999
The adsorption of a near-critical fluid confined in a slit pore is investigated by means of densi... more The adsorption of a near-critical fluid confined in a slit pore is investigated by means of density functional theory and by Monte Carlo simulation for a Lennard-Jones fluid. Our work was stimulated by recent experiments for SF6 adsorbed in a mesoporous glass, which showed the striking phenomenon of critical depletion, i.e., the adsorption excess Gamma first increases but then decreases very rapidly to negative values as the bulk critical temperature T(c) is approached from above along near-critical isochores. By contrast, our density functional and simulation results, for a range of strongly attractive wall-fluid potentials, show Gamma monotonically increasing and eventually saturating as the temperature is lowered toward T(c) along both the critical (rho=rho(c)) and subcritical isochores (rho<rho(c)). Such behavior results from the increasingly slow decay of the density profile away from the walls, into the middle of the slit, as T-->T(+)(c). For rho<rho(c) we find that i...
ChemInform, 2003
We survey the portfolio of computational strategies available for tackling the generic problems o... more We survey the portfolio of computational strategies available for tackling the generic problems of phase behavior -free-energy-estimation and coexistence-curve mapping.
Chemical Physics, 2006
We report a phase switch Monte Carlo (PSMC) method study of the freezing line of the Lennard-Jone... more We report a phase switch Monte Carlo (PSMC) method study of the freezing line of the Lennard-Jones (LJ) fluid. Our work generalizes to soft potentials the original application of the method to hard-sphere freezing and builds on a previous PSMC study of the LJ system by Errington [J. Chem. Phys. 120, 3130 (2004)]. The latter work is extended by tracing
We describe a Monte Carlo scheme for simulating polydisperse uids within the grand canonical ense... more We describe a Monte Carlo scheme for simulating polydisperse uids within the grand canonical ensemble. Given some polydisperse attribute , the state of the system is described by a density distribution ( ) whose form is controlled by the imposed chemical potential distribution ( ). We detail how histogram extrapolation techniques can be employed to tune ( ) such as
Physical Review E, 2007
Fluids in which the interparticle potential has a hard core, is attractive at moderate separation... more Fluids in which the interparticle potential has a hard core, is attractive at moderate separations, and repulsive at greater separations are known to exhibit novel phase behavior, including stable inhomogeneous phases. Here we report a joint simulation and theoretical study of such a fluid, focusing on the relationship between the liquid-vapor transition line and any new phases. The phase diagram
American Journal of Physics, 2001
The task of accurately locating fluid phase boundaries by means of computer simulation is hampere... more The task of accurately locating fluid phase boundaries by means of computer simulation is hampered by problems associated with sampling both coexisting phases in a single simulation run. We explain the physical background to these problems and describe how they can be tackled using a synthesis of biased Monte Carlo sampling and histogram extrapolation methods, married to a standard fluid
Journal of Physics-condensed Matter, 1997
We review and discuss recent advances in the simulation of bulk critical phenomena in model fluid... more We review and discuss recent advances in the simulation of bulk critical phenomena in model fluids. In particular we emphasize the extensions to finite-size scaling theory needed to cope with the lack of symmetry between coexisting fluid phases. The consequences of this asymmetry for simulation measurements of quantities such as the particle density and the heat capacity are pointed out
The Journal of Chemical Physics, 2014
In a cluster crystal, each lattice site is occupied by multiple soft-core particles. As the numbe... more In a cluster crystal, each lattice site is occupied by multiple soft-core particles. As the number density is increased at zero temperature, a 'cascade' of isostructural phase transitions can occur between states whose site occupancy differs by unity. For low but finite temperature, each of these transitions terminates in a critical point. Using tailored Monte Carlo simulation techniques we have studied such demixing cascades in systems of soft particles interacting via potentials of the generalized exponential form u(r) = exp[−(r/σ) n ]. We have estimated the critical parameters of the first few transitions in the cascade as a function of the softness parameter n. The critical temperature and pressure exhibit non-monotonic behaviour as n is varied, although the critical chemical potential remains monotonic. The trends for the pressure and chemical potential are confirmed by cell model calculations at zero temperature. As n → 2 + , all the transitions that we have observed are preempted by melting although we cannot rule out that clustering transitions survive at high density.
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Papers by Nigel B Wilding