The current description of how light particles (electrons and positrons) travel around inside of liquids is quite complex. The interactions with many molecules simultaneously means we must understand collective phenomena: phonons, excitons and screened collisions. What's more, light particles show off their quantum nature at low energies, with de Broglie wavelengths that extend over multiple molecules so the typical classical view of electrons “bouncing off” molecules is not well justified. In short, understanding and simulating the motion of electrons or positrons in liquids is difficult.
However, there is an even more fundamental property that is not well understood: what is the minimum energy that these particles can have in a liquid? This property, V0, is referred to by many names as the “background energy”, the “liquid energy” or even the “work function”.
Knowing the value of the background energy and how it varies with density of the liquid is essential in many theories. It is needed to understand reflection/penetration at gas/liquid interfaces, it modifies the rates of scattering inside a liquid and it is crucial to understanding self-trapping whereby an electron or positron stabilises in a bubble or cluster inside the liquid.
One possible method to calculate the background energy is the local Wigner-Seitz model pioneered by Evans, Findley and collaborators at Queens College in New York and University of Louisiana. This model has been very successful, however it relies on one fitting parameter and the experiments that allow them to set this parameter cannot be performed for positrons. We seek to extend this model to ab initio potentials and obtain background energies of positrons in liquids.