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In recent years much interest has been shown in the process of thermohalinemixing in red giants. In low and intermediate mass stars this mechanism firstactivates at the position of the bump in the luminosity function, and has beenidentified as a likely candidate for driving the slow mixing inferred to occurin these stars. One particularly important consequence of this process, whichis driven by a molecular weight inversion, is the destruction of lithium. Weshow that the degree of lithium destruction, or in some cases production, isextremely sensitive to the numerical details of the stellar models. Within thestandard 1D diffusion approximation to thermohaline mixing, we find thatdfferent evolution codes, with their default numerical schemes, can producelithium abundances that differ from one another by many orders of magnitude.This disagreement is worse for faster mixing. We perform experiments with fourindependent stellar evolution codes, and derive conditions for the spatial andtemporal resolution required for a converged numerical solution. The resultsare extremely sensitive to the timesteps used. We find that predicted lithiumabundances published in the literature until now should be treated withcaution.

On the Numerical Treatment and Dependence of Thermohaline Mixing in Red Giants