Improved parameterization of the bridge function of one-component plasma liquids
Title: Improved parameterization of the bridge function of one-component plasma liquids
SNIC Project: SNIC 2020/5-340
Project Type: SNIC Medium Compute
Principal Investigator: Svetlana Ratynskaia <>
Affiliation: Kungliga Tekniska högskolan
Duration: 2020-07-01 – 2021-03-01
Classification: 10304 10303


The newly-proposed isomorph-based empirically modified hypernetted-chain (IEMHNC) approach is capable of reproducing the structural and thermodynamic properties of Yukawa and bi-Yukawa liquids with an unprecedented combination of accuracy and computational speed. This integral equation theory approach utilizes an isentropic mapping between Yukawa/bi-Yukawa & Coulomb state points and also requires the bridge function of one-component plasma (OCP) as an input. Nominally exact OCP bridge functions were previously extracted from Monte Carlo simulations and closed form expressions via the coupling parameter were suggested. Our recent work has indicated that the bin widths used in the determination of the radial distribution functions were too large for the task; translating to very small grid errors in the radial distribution function but unacceptably large grid errors in the highly sensitive bridge function. Our recent work has also demonstrated that the reduced excess entropy constitutes a better independent state variable than the coupling parameter as far as closed-form bridge function expressions are concerned. In this project, we intend to a) Extract OCP bridge functions with a combination of large-statistics NVT MD simulations and specially designed biased MD simulations. Our methodology has been extensively tested with Yukawa potentials, n>3 IPL potentials, EXP potentials and Lennard-Jones potentials. Hence, minor complications in the OCP could only arise from the implementation of the Ewald sum. b) Compute the reduced excess entropy (via the reduced excess chemical potential) with the recently developed spatially resolved thermodynamic integration strategy that avoids the use of enhanced sampling techniques whose implementation might turn out to be problematic for dense liquids. The above input will allow for a highly accurate parameterization of the exact OCP bridge function, which is expected further increase the already high accuracy of the IEMHNC approach on par with computer simulations.