We address, by means of ab-initio calculations, the origin of the correlation that has been observed experimentally between the chemisorption energy of CO on nanoscale Cu(001) supported films and quantum-size effects. The calculated chemisorption energy shows systematic oscillations, as a function of film thickness, with a periodicity corresponding to that of quantum-well states at Γ crossing the Fermi energy. We explain this trend based on the oscillations, with film thickness, of the decay length on the vacuum side of the quantum-well states at the Fermi energy. Contrary to previous suggestions, we find that the actual oscillations with film thickness of the density of states per atom of the film at the Fermi energy cannot account for the observed trend in the chemisorption energy.

Recent experimental investigations into the magnetic properties of V/Gd bilayers have shown that vanadium, which is nonmagnetic in the bulk, can acquire a magnetic moment in such systems. We have performed ab initio pseudopotential calculations to examine the magnetic behavior of V(110)/Gd(0001) bilayers for V layers with thicknesses up to 4 monolayers (ML). We considered both abrupt and atomic intermixed V/Gd interfaces. In both cases, the magnetic moment of the V layer is found to align antiparallel to the moment of the Gd layer, consistent with the experimental observation. However, the magnitude of the V moment at the abrupt interface is considerably smaller than the moments reported experimentally. In the presence of atomic intermixing, instead, substantially larger V moments are found, closer to the experimentally reported moments. On the basis of the calculated atomic and spin resolved density of states, we discuss the possible mechanism responsible for the observed Gd-V antiferromagnetic coupling.

Density functional theory calculations within a DFT+U approach have been carried out to determine the effect of hydrostatic pressure and strain on the structural, electronic and magnetic properties of La0.75Ca0.25MnO3. We investigate the opportunuty of the appearence of the A-type antiferromagnetic phase under pressure as observed from experiments. At ambient pressure and in the hydrostatic pressure regime (4–25 GPa), the system remains ferromagnetic in its ground state, and the A-type antiferromagnetic coupling is tied to Mn e g orbital order while the ferromagnetic behavior refers to orbital disorder one. No magnetic transition was found when increasing the hydrostatic pressure up to 25 GPa. Applying a tetragonal distortion along the b direction of the pnma orthorhombic structure, the system exhibits a transition from the ferromagnetic orbitally disordered phase to the A-type antiferromagnetic orbitally ordered phase at about 22.5 GPa, in agreement with experiment. Projected density of states (PDOS) calculations predict the pressure and strain effects that are discussed in terms of different electronic occupations through d x 2 − y 2 and d 3 z 2 − r 2 orbitals.