Cluster velocity distributions in a vapor at equilibrium

Abstract

We present the microscopic description of the vapor using the concept of cluster. Taking into consideration nonideal contributions, the distribution functions of every cluster species are obtained. From these distribution functions it is possible to derive kinetic “temperatures” associated with each cluster species and it is shown that the internal kinetic temperature and the kinetic temperature associated with the center of mass of the clusters are different from the thermodynamic temperature of the system as a whole. Molecular dynamic simulations show that the internal temperatures are smaller than the thermodynamic one, which is smaller than the kinetic temperatures for all cluster sizes. For the case of monomers more precise predictions can be made and they are in excellent agreement with our simulations.

Continuum percolation of simple fluids: energetic connectivity criteria

“…We add a maximum connectivity distance d to the criteria to avoid unrealistic bonding. Two particles separated by a distance greater than this maximum distance are considered as non-bonded even if their relative velocity is by chance zero [16]. We show that the velocity average introduces an important overestimation on the predicted percolation density at all temperatures.…”

“…More recently, Hill's criterion has been reconsidered in molecular dynamics studies of small clusters [15,16] and the critical percolation behaviour of Lennard-Jones fluids [17]. It has been suggested that the percolation line − the line that separates the temperature-density phase space into percolated and non-percolated states − might be experimentally observable [17,18].…”

Cluster birth–death processes in a vapor at equilibrium

“…22 One can also require that, besides proximity, the particles satisfy some energy requirement associated to the idea of forming a bound state. 23,24 These energetic clusters were proposed as better candidates to have a dynamic theory of vapors, but they have nonclassical kinetic properties. For example, at equilibrium their velocity distribution function is not Maxwellian.…”

“…23 The kinetic origin of memory effects come from dealing with clusters simply classified by their size without taking into consideration quite different dynamic characteristics ͑such as angular momentum or internal energy͒ between them. To have local equations, the clusters must be classified according to the values of their degrees of freedom, requiring a kinetic approach by means of kinetic equations.…”

Cluster pair correlation function of simple fluids: Energetic connectivity criteria

“…27 It should be mentioned that the HE criterion has been considered in MD studies of small clusters and the critical percolation behavior of Lennard-Jones fluids by several authors. 28,29,30 It has been suggested that the percolation line-the line that separates the temperature-density phase diagram into percolated and non-percolated states-might be experimentally observable. 30,31 Moreover, cluster analysis based on this criterion seems to be useful in locating the gas-liquid coexistence curve.…”