Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: A density-functional theory study

Yanfang Li; Ping Zhang; Bo Sun; Yu Yang; Yinghui Wei

paper

Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: A density-functional theory study

arXiv:0904.4387

Abstract

We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage and adsorption sites. In the coverage range $0 < Θ < 1.0, t h e m os t s t ab l e am o n g a l l p oss ib l e a d sor pt i o n s i t es i s t h eo n - s u r f a ce f ccs i t e f o l l o w e d b y t h e h c p s i t e, an d t h e bin d in g e n er g y in cr e a ses w i t h t h eco v er a g e, t h u s in d i c a t in g t h e hi g h er s t abi l i t y o f o n - s u r f a ce a d sor pt i o nan d a t e n d ecy t o t h e f or ma t i o n o f H i s l an d s (c l u s t er s) w h e nin cr e a s in g t h eco v er a g e w i t hin t h er e g i o n$ 0<Θ<1.0. The on-surface diffusion path energetics of atomic hydrogen, as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites, are also presented at low coverage. At high coverage of $1.00 < Θ < 2.0, i t i s f o u n d t ha tt h eco a d sor pt i o n co n f i g u r a t i o n w i t h 1.0 m o n o l a y er o f H^{'} sr es i d in g o n t h es u r f a ce f ccs i t es an d t h er e mainin g m o n o l a y er o f H^{'} socc u p y in g t h es u b s u r f a ce t e t r a - I s i t es i s m os t e n er g e t i c a l l y f a v o u r ab l e . T h er es u l t an t H - M g - H s an d w i c h s t r u c t u r e f or t hi s m os t s t ab l eco a d sor pt i o n co n f i g u r a t i o n d i s pl a y ss imi l a r s p ec t r a l f e a t u r es t o t h e b u l k h y d r i d e M g H$ _{2}$ in the density of states. The other properties of the H/Mg(0001) system, including the charge distribution, the lattice relaxation, the work function, and the electronic density of states, are also studied and discussed in detail. It is pointed out that the H-Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.

21 pages, 10 figures