A new truncation scheme for BBGKY hierarchy: conservation of energy and time reversibility

TL;DR

This paper introduces a novel truncation scheme for the BBGKY hierarchy that conserves energy and maintains time reversibility, simplifying the kinetic equations for many-particle systems.

Contribution

The paper presents a new truncation method for the BBGKY hierarchy that ensures energy conservation and time symmetry, connecting to existing models and hierarchies.

Findings

Reduces to Martys' model for velocity independent correlations

Recovers BGY hierarchy in steady state

Proves energy conservation and time reversibility of the scheme

Abstract

We propose a new truncation scheme for Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. We approximate the three particle distribution function $f_{3}(1,2,3,t)$ in terms of $f_{2}(1,2,t)$, $f_{1}(3,t)$ and two point correlation functions $\left\lbrace g_{2}(1,3,t), g_{2}(2,3,t)\right\rbrace $. Further $f_{2}$ is expressed in terms of $f_{1}(1,t)$ and $g_{2}(1,2,t)$ to close the hierarchy, resulting a set of coupled kinetic equations for $f_{1}$ and $g_{2}$. In this paper we show that, for velocity independent correlations, the kinetic equation for $f_{1}$ reduces to the model proposed by Martys[Martys N S 1999 \textit{IJMPC} \textbf{10} 1367-1382]. In the steady state limit, the kinetic equation for $g_{2}$ reduces to Born-Green-Yvon (BGY) hierarchy for homogeneous density. We also prove that the present scheme respects the energy conservation and under specific circumstances, time symmetry \textit{i.e.,} $\displaystyle \frac{dH(t)}{dt} = 0$ where $H(t)$ refers to the Boltzmann's H-function.