Mojmír Tomášek

Simple comments on the W(001) surface instability

Abstract A geometrical interpretation of the reconstruction of the ideal W(001) surface is suggested, which is based on the use of the generalized Huckel rule. More complicated situations like steps are also mentioned and it is speculated that the increase in the coordination of the surface atom does not mean necessarily an increase in its stability.

Simple analysis of an important bonding mechanism in the W(001) reconstruction

Abstract The interaction of two transition metal adatoms at the ideal (001) surface of a bcc transition metal, formed by the same sort of atoms, is studied by means of the recursion method. For approximately half-filled electronic bands, the adatom dimer stability is reduced due to indirect interactions (three- and four-body terms, fourth moment effects). This result is interpreted by using the “generalized Huckel rule” and the oscillation theorems based on the theory of moments. It is believed that the results offer further insight into the W(001) reconstruction problem.

A note on the Hohenberg-Kohn theorem

Abstract An alternative, concise proof of the general form of Hohenberg-Kohn theorem is presented.

Some simple ideas about instability and reconstruction of the W(001) surface

Abstract Simple qualitative reasoning based on symmetry arguments is used to study the reconstruction of the W(001) surface. It is assumed that the inherent lattice instability is caused mainly by electron-phonon coupling via Shockley surface states from the vicinity of the Fermi energy. The introduction of the local C 4v symmetry enables to analyze the respective electron-phonon matrix elements and leads to the conclusion that in-plane reconstruction modes M 5 and X 3 are more perspective than the buckled ones.

On the nonideal atom arrangements at the W (001) surface

Abstract Various nonideal atom arrangements (steps, vacancy, adatoms, etc.) at the W (001) surface are studied within a simple LCAO scheme. All the atoms reside in the ideal bulk-like positions. It appears that the energy differences can be related to two- and three-body interactions, which are approximately additive for atoms with a fixed number of first-nearest neighbours. The ideal (1 × 1) surface is less stable than some of its defect forms. The most probable mechanism of the stabilization near the step edges seems to be an expansion.

On the stability of the W(001) surface

Abstract Recently, the present authors have suggested that some of the basic features of the unstable W(001)-(1×1) surface can be explained by the competition between the direct attractive and indirect repulsive interactions present at the surface. To understand this mechanism in more detail, number of surface structures (steps in the (0,1) and (1,1) direction, vacancy, adatoms etc.) have been investigated within a simple LCAO recursion scheme. The direct interactions (two-body term) and the indirect ones (three-body terms) are approximately additive for surface atoms and adatoms having four nearest neighbours. The unreconstructed (1×1) surface is under compressive (repulsive) stress and we suggest that, for example, steps should expand near their edges.

Local density of states of GaAs and InAs surfaces: Ideal (111), (001) and (110) surfaces and monoatomic steps on the (111) and the (001) surface

The ideal (111), (001) and (110) surfaces of GaAs and InAs are investigated by means of the LCAO Green function recursion method to obtain local density of states. Main emphasis is laid on the analysis of the nature and character of the inherent surface states. For this purpose, several imperfections on the (111) and the (001) surface (i.e. vacancies and steps with varying topology) are treated to demonstrate the local character of Shockley surface states and to confirm their chemical nature. The applicability of the results obtained to other A3B5 compounds is discussed. Comparison with experiment and other theoretical investigations is also made.