Résumé
Context. A precision of the order of one percent is needed on the parameters of exoplanet-hosts stars to correctly characterise the planets themselves. This can be achieved by asteroseismology. It is important in this context to test the influence of introducing atomic diffusion with radiative accelerations in the models upon the derived parameters. In this paper, we begin this study with the case of the star 94 Ceti A.Aims. We aim to perform a complete asteroseismic analysis of the exoplanet-host F-type star 94 Ceti A, from the first radial-velocity observations with the High Accuracy Radial velocity Planet Searcher (HARPS) up to the final computed best models. We also aim to test the influence of atomic diffusion, including radiative accelerations, upon the computed frequencies and on the determined stellar parameters. 94 Ceti A is hot enough to suffer these effects. We also aim to test the effect of including a complete atmosphere in the stellar models.Methods. The radial velocity observations were performed with HARPS in 2007. The low degree modes were derived and identified using classical methods and compared with the results obtained from stellar models computed with the Toulouse Geneva Evolution Code (TGEC).Results. We obtained precise parameters for the star 94 Ceti A. We showed that including atomic diffusion with radiative accelerations can modify the age by a few percent, whereas adding a complete atmosphere does not change the results by more than one percent. Conclusions. Atomic diffusion including radiative accelerations should be taken into account in all the computations of stellar models with masses larger than 1.3 M⊙ in order to determine accurate parameters for observed stars.