Measuring Many-Body Distribution Functions in Fluids using Test-Particle Insertion

将粒子插入活性流体中的功

Work to insert a particle into an active fluid

本文研究了将粒子插入活性流体所需的功，发现该功依赖于活动性、密度和插入协议，并观察到即使缓慢插入，功波动仍保留非高斯尾部，且密度与功之间存在相反趋势。

Model-free measurement of the pair potential in colloidal fluids using optical microscopy

We report a straightforward, model-free approach for measuring pair potentials from particle-coordinate data, based on enforcing consistency between the pair distribution function measured separately by the distance-histogram and test-particle insertion routes. We demonstrate the method's accuracy and versatility in simulations of simple fluids, before applying it to an experimental system composed of superparamagnetic colloidal particles. The method will enable experimental investigations into many-body interactions and allow for effective coarse-graining of interactions from simulations.

Chemical Potential Calculations In Dense Liquids Using Metadynamics

The calculation of chemical potential has traditionally been a challenge in atomistic simulations. One of the most used approaches is Widom's insertion method in which the chemical potential is calculated by periodically attempting to insert an extra particle in the system. In dense systems this method fails since the insertion probability is very low. In this paper we show that in a homogeneous fluid the insertion probability can be increased using metadynamics. We test our method on a supercooled high density binary Lennard-Jones fluid. We find that we can obtain efficiently converged result…

Monte-Carlo rejection as a tool for measuring the energy landscape scaling of simple fluids

A simple modification of the Monte-Carlo algortihm is proposed to explore the topography and the scaling of the energy landscape. We apply this idea to a simple hard-core fluid. The results for different packing fractions show a power law scaling of the landscape boundary, with a characteristic scale that separates the values of the scaling exponents. Finally, it is shown how the topology determines the freezing point of the system due to the increasing importance and complexity of the boundary.

Chemical potential of a test hard sphere of variable size in a hard-sphere fluid

The Labík and Smith Monte Carlo simulation technique to implement the Widom particle insertion method is applied using Molecular Dynamics (MD) instead to calculate numerically the insertion probability, $P_0(η,σ_0)$, of tracer hard-sphere (HS) particles of different diameters, $σ_0$, in a host HS fluid of diameter $σ$ and packing fraction, $η$, up to $0.5$. It is shown analytically that the only polynomial representation of $-\ln P_0(η,σ_0)$ consistent with the limits $σ_0\to 0$ and $σ_0\to\infty$ has necessarily a cubic form, $c_0(η)+c_1(η)σ_0/σ+c_2(η)(σ_0/σ)^2+c_3(η)(σ_0/σ)^3$. Our MD data f…

Measuring local volume fraction, long-wavelength correlations and fractionation in a phase-separating polydisperse fluid

We dynamically simulate fractionation (partitioning of particle species) during spinodal gas-liquid separation of a size-polydisperse colloid, using polydispersity up to ~40% and a skewed parent size distribution. We introduce a novel coarse-grained Voronoi method to minimise size bias in measuring local volume fraction, along with a variety of spatial correlation functions which detect fractionation without requiring a clear distinction between the phases. These can be applied whether or not a system is phase separated, to determine structural correlations in particle size, and generalise eas…