DENSITY-FUNCTIONAL THEORY STUDY OF NA ON AL(111) AND O ON RU(0001)

The success of density functional theory for the description of the ad sorption of atoms on surfaces is well established and, based on recent calculations using gradient corrections, it has been shown that it al so describes well the dissociative adsorption of molecules at surfaces - admittedly, however, the database for reactions at surfaces is stil l somewhat small. In this paper the power of density functional theory calculations is demonstrated through investigations for two different adsorption systems, namely one with a strongly electropositive adsorb ate [Na on Al(111)] and one with a strongly electronegative adsorbate [O on Ru(0001)]. In each case, new hitherto unexpected adsorbate phase s have been predicted by the theory: for Na on Al(111) the stability o f a ''four-layer'' surface alloy was identified while for O on Ru(0001 ) it was predicted that the formation of a (1 x 1)-O adlayer should be possible which implies that the apparent saturation coverage of Theta (o) = 1/2 is due to kinetic hindering.