Simulation study of isotopic effect on properties of liquid lithium

Among pure metals, lithium is the one with the highest mass ratio between existing stable isotopes. In this study, we use classical molecular dynamics (MD) simulations in order to determine the sensitivity of different properties to the presence of these two isotopes. The isotopic effect occurs in two ways: the first one is the direct influence of the mass of the atom on its motion while the second one is the influence of the composition of its environment. For this purpose, we consider several samples which composition changes from 100%⁶Li to 100%⁷Li. We first focus on the static structure which, as could be expected, is not affected by the isotopic mass since the interatomic forces are independent on the isotopic species. This is not the case when considering the self-diffusion coefficients, the viscosity or the dynamic structure factor. The differences between behaviours of both species are highlighted and their influence on the measured properties is discussed. The comparison with available experimental data raises the question of the possible existence of quantum effects in lithium. Unfortunately, MD simulations cannot account for such effects. For both isotopic or quantum effects, this study brings out the need for further experimental studies.