We have studied the properties of quantum well states in supported Ag(100) films on the Fe substrate by first-principles density-functional calculations. The energies of these quantum well states as a function of thickness N are examined in terms of the characteristic phase shift of the electronic wave function at the interface. These energy-dependent phase shifts are determined numerically for both the film-substrate and film-vacuum interfaces. It is also found that the substrate has a major effect on film stability, enhancing the stability of the N=5 film and reversing that of the N=2 film.

We have studied the properties of quantum well states in supported Ag(100) films on the Fe substrate by first-principles density-functional calculations. The energies of these quantum well states as a function of thickness N are examined in terms of the characteristic phase shift of the electronic wave function at the interface. These energy-dependent phase shifts are determined numerically for both the film-substrate and film-vacuum interfaces. It is also found that the substrate has a major effect on film stability, enhancing the stability of the N=5 film and reversing that of the N=2 film.

Quasiparticle band structures for the cubic trihydrides YH3 and LaH3 have been calculated by evaluating the self-energy in the GW approximation using ab initio pseudopotentials and plane waves. These are the prototype metal hydrides that exhibit switchable optical properties. For both materials, the local-density approximation (LDA) yields semimetallic energy bands with a direct overlap of about 1 eV. We find the self-energy correction to the LDA energies opens a gap at Gamma of 0.8-0.9 eV for LaH3 and 0.2-0.3 eV for YH3, where the latter is in sharp contrast to a previous study using linear-muffin-tin orbitals. The quasiparticle band gaps are analyzed as a function of an initial shift in the LDA bands used to evaluate the random-phase approximation screening in constructing the self-energy. We also make a comparison of results obtained by using two different pseudopotentials, each designed to better approximate exchange and correlation between the semicore states and valence states of Y and La.

We present first-principles calculations that provide a detailed diffusion picture of an adsorbed Si atom on the Si(111)-(7x7) surface. Several diffusion paths for the adsorbed Si atom are established by mapping out the total energy as a function of its positions on the surface. For diffusion between the faulted and unfaulted halves, the energy barriers range from 0.96 to 1.21 eV, while remarkable low-energy barriers from 0.3 to 0.7 eV are discovered within the faulted and unfaulted regions.

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.