23 research outputs found
Adsorption and dissociation of O at Be(0001): First-principles prediction of an energy barrier on the adiabatic potential energy surface
The adsorption and dissociation of O molecules at the Be(0001) surface
is studied by using density-functional theory within the generalized gradient
approximation and a supercell approach. The physi- and chemisorbed molecular
precursor states are identified to be along the parallel and vertical channels,
respectively. It is shown that the HH-Z (see the text for definition) channel
is the most stable channel for the molecular chemisorption of O. The
electronic and magnetic properties of this most stable chemisorbed molecular
state are studied, which shows that the electrons transfer forth and back
between the spin-resolved antibonding molecular orbitals and the
surface Be states. A distinct covalent weight in the molecule-metal bond
is also shown. The dissociation of O is determined by calculating the
adiabatic potential energy surfaces, wherein the T-Y channel is found to be the
most stable and favorable for the dissociative adsorption of O.
Remarkably, we predict that unlike the other simple metal surfaces such as
Al(111) and Mg(0001), the \textit{adiabatic} dissociation process of O at
Be(0001) is an activated type with a sizeable energy barrier.Comment: 21 pages, 10 figure
Rotation of hydrogen molecules during the dissociative adsorption on the Mg(0001) surface: A first-principles study
Using first-principles calculations, we systematically study the potential
energy surfaces and dissociation processes of the hydrogen molecule on the
Mg(0001) surface. It is found that during the dissociative adsorption process
with the minimum energy barrier, the hydrogen molecule firstly orients
perpendicular, and then rotates to be parallel to the surface. It is also found
that the orientation of the hydrogen molecule at the transition state is
neither perpendicular nor parallel to the surface. Most importantly, we find
that the rotation causes a reduction of the calculated dissociation energy
barrier for the hydrogen molecule. The underlying electronic reasons for the
rotation of the hydrogen molecule is also discussed in our paper.Comment: 14 pages, 4 figure