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A series of recent theoretical atomic diffusion studies has address thechallenging problem of predicting inhomogeneous vertical and horizontalchemical element distributions in the atmospheres of magnetic ApBp stars. Herewe critically assess the most sophisticated of such diffusion models - based ona time-dependent treatment of the atomic diffusion in a magnetised stellaratmosphere - by direct comparison with observations as well by testing thewidely used surface mapping tools with the spectral line profiles predicted bythis theory. We show that the mean abundances of Fe and Cr are grosslyunderestimated by the time-dependent theoretical diffusion model, withdiscrepancies reaching a factor of 1000 for Cr. We also demonstrate thatDoppler imaging inversion codes, based either on modelling of individual metallines or line-averaged profiles simulated according to theoreticalthree-dimensional abundance distribution, are able to reconstruct correcthorizontal chemical spot maps despite ignoring the vertical abundancevariation. These numerical experiments justify a direct comparison of theempirical two-dimensional Doppler maps with theoretical diffusion calculations.This comparison is generally unfavourable for the current diffusion theory, asvery few chemical elements are observed to form overabundance rings in thehorizontal field regions as predicted by the theory and there are numerousexamples of element accumulations in the vicinity of radial field zones, whichcannot be explained by diffusion calculations.

Putting atomic diffusion theory of magnetic ApBp stars to the test: evaluation of the predictions of time-dependent diffusion models