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Observations suggest that a relationship exists between the driving mechanismof roAp star pulsations and the heavy element distribution in these stars. Weattempt to study the effects of local and global metallicity variations on theexcitation mechanism of high order p-modes in A star models. We developedstellar evolutionary models to describe magnetic A stars with different globalmetallicity or local metal accumulation profiles. These models were computedwith CLES ("Code Li\`egeois d'\'evolution stellaire"), and the stability of ourmodels was assessed with the non-adiabatic oscillation code MAD. Our modelsreproduce the blue edge of the roAp star instability strip, but generate a rededge hotter than the observed one, regardless of metallicity. Surprisingly, wefind that an increase in opacity inside the driving region can produce a loweramount of driving, which we refer to as the "inverse $\kappa$-mechanism".

New light on the driving mechanism in roAp stars. Part I. Effects of metallicity