Long ago, Allan suggested that the V(001) surface could be magnetic even if bulk vanadium is not. Later on, Freeman realized an ab‐initio calculation (FLAPW) and got that the V(001) surface is not magnetic. Experiments by Rau and co‐workers gave a finite magnetic moment and the question whether V(001) is magnetic or not was never settled. In this work, we face two aspects of this problem. In the first part, we explore with a tight‐binding model the effect of the difference of 5.3% on the theoretical lattice parameter as compared to experiment. In the second part, we look at the effect that the contraction of the first interlayer distance has on the electronic structure at the surface. According to our results the possibility of a contraction up to 5% is worth studying in more detail since an overall acceptable agreement between experiment and theory seems to be more realistic in this way.
Transition probabilities on the interaction of the ground and the lowest excited states of gold Au ((2)S:5d(10)6s(1), (2)D:5d(9)6s(2), and (2)P:5d(10)6p(1)) with silane (SiH(4)) are studied through ab initio Hartree-Fock self-consistent field calculations, where the atom's core is represented by relativistic effective core potentials. These calculations are followed by a multiconfigurational self-consistent field study. The correlation energy is accounted for through extensive variational and perturbative second order multireference Moller-Plesset configuration interaction analysis of selected perturbations obtained by iterative process calculations using the CIPSI program package. It is found that the Au atom in the ((2)P:5d(10)6p(1)) state inserts in the Si-H bond. In this interaction its corresponding D (2)A(') potential energy surface is initially attractive and only becomes repulsive after encountering an avoided crossing with the initially repulsive C (2)A(') surface linked to the Au((2)D:5d(9)6s(2))-SiH(4) fragments. The A, B, and C (2)A(') curves derived from the Au((2)D:5d(9)6s(2)) atom interaction with silane are initially repulsive, each one of them showing two avoided crossings, while the A (2)A(') curve goes sharply downwards until it meets the X (2)A(') curve interacting adiabatically, which is linked with the Au((2)S:5d(10)6s(1))-SiH(4) moieties. The A (2)A(') curve becomes repulsive after the avoided crossing with the X (2)A('), curve. The lowest-lying X (2)A(') potential leads to the HAuSiH(3) X (2)A(') intermediate molecule. This intermediate molecule, diabatically correlated with the Au((2)P:5d(10)6p(1))+SiH(4) system which lies 3.34 kcal/mol above the ground state reactants, has been carefully characterized as have the dissociation channels leading to the AuH+SiH(3) and H+AuSiH(3) products. These products are reached from the HAuSiH(3) intermediate without any activation barrier. The Au-SiH(4) calculation results are successfully compared to experiment. Landau-Zener theory of avoided crossings is applied to these interactions considering the angle theta instead of the distance r as the reaction coordinate.
We study the magnetic behavior of a 4d transition-metal Ru monolayer (ML) on different substrates and orientations. In the ground state, an ideal Ru-ML is expected to be ferromagnetic on Ag(001) and Au(001) with a magnetic moment, µ, around 1.7 µB (Bohr magnetons) in both cases. On Cu(001), a Ru-ML is not magnetic. In this paper, we study the magnetic behavior of a Ru-ML at other orientations, i.e., (110) and (111), and analyze the phenomenon as a whole. We find magnetism on Au(111), and Ag(111) (µ ≈ 1 µB for both) but no magnetic activity on a Cu substrate in any orientation. This gives the first impression that the lattice parameter of the substrate is the one that governs the switching on of magnetism in the Ru-ML. But then, we find that on both Ag(110) and Au(110), an ideal Ru-ML is not magnetic. For that reason, we have tried to find another geometric parameter that would correlate better with the magnetic moment. We find that neither the total number of first nearest neighbors for each orientation, nor the number of them on the ML, or the number of them in the substrate, or the area per atom on the ML, correlate. We find a correlation with a parameter, Ω0, that represents the volume per atom in the monolayersubstrate interface region. But this parameter seems to have the wrong trend according to intuition. Further analysis shows that the details of the interaction are important, and that the physics underlying the switching on of magnetism in a Ru-ML on noble metal substrates, is determined by an intraband transfer of d-electronic states, from lower and higher energies to the Fermi level, that enhances the density of states at that energy, in an important way. This depends on specificities of the interaction between the ML and the substrate that are hardly taken into account by a single parameter that is merely geometric. PACS Nos.: 75.10b, 75.30m, 75.70.Ak, 73.20.At
Proper planning and coordination allowed the hospital to be moved without incidents and without decreasing activity.
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