Analysis of the First Bridge Diagram of Liquid Bromine

Sebastian Rast,^1,3,* Pascal H. Fries² and Hartmut Krienke¹

¹ Institut für Physikalische und Theoretische Chemie der Universität Regensburg, D–93049 Regensburg, Germany
² CEA, INAC, SCIB (UMR_E 3, CEA, UJF), Laboratoire de Reconnaissance Ionique et de Chimie de Coordination, F–38054 Grenoble, France
³ now at Max Planck Institute for Meteorology, Bundesstr. 53, D–20146 Hamburg, Germany
* Corresponding author: E-mail: sebastian.rast@zmaw.de

Abstract
The first bridge diagrams of the classical theory of liquids are discussed for two fluids of Lennard-Jones spheres and for a fluid of a two-centre Lennard-Jones model of liquid bromine. The bridge diagram of liquid bromine is calculated using a biased Monte-Carlo method. We investigate the first bridge diagrams, the bonds of which are either Mayer functions f or total correlation functions h. The Mayer f-bond representation leads to very high values of the first bridge diagram, which can not be used alone in a truncated expansion of the diagrammatic series of the bridge function. We analyse the origin of these high values. In the case of the h-function representation, the bridge function series truncated to the sole first bridge diagram is introduced into the closure of the Ornstein-Zernike equation and leads to some improvement of the pair distribution function upon the HNC result, as compared to the exact simulated values.

Keywords: Bridge function, molecular Ornstein-Zernike equation, liquid bromine