H. J. F. Jansen

Structural, electronic and magnetic properties of NiAl and FeAl alloys☆

Abstract Local density total energy and electronic structure calculations for NiAl, Ni 3 Al, FeAl and Fe 3 Al yield lattice constants which agree well with experiment. We find for Ni 3 Al the Cu 3 Au structure, and for Fe 3 Al the DO 3 structure as their ground states, NiAl is paramagnetic, Fe 3 Al ferromagnetic, and Ni 3 Al and FeAl show weak itinerant magnetic phases.

Local density total energy description of ground and excited state properties of the rare earth metals

Abstract Ground and excited state properties of rare-earth metals are investigated by means of total energy calculations in the local density approximation using the linearized muffin-tin orbital band structure method. Equilibrium lattice constants, bulk moduli and cohesive energies obtained for the rare-earth series are found to be in good agreement with experimental trends. The localization of the 4f electrons in the rare-earths is discussed and compared with that of the 5f electrons in the actinides. The relation between the structural sequence observed in the rare-earths and d-band occupancy is examined. The 4f excitation energies and intra-atomic Coulomb correlations—obtained by taking the difference in total energy of the appropriate final states—are compared with the results of photoemission and inverse photoemission experiments. A comparison of the localization of the 4f electrons in the rare-earths with that of the 5f electrons in the actinides is presented using additional results obtained for the actinide metals with the same approach.

A Monte Carlo Calculation of the Nematic-Isotropic Phase Transition

Abstract The behaviour of a lattice version of the Maier-Saupe model near the clearing point is investigated using a biased Monte Carlo technique. The lattice version consists of an array of unit vectors, which are located at the sites of a n x n x n (n = 14, 16, 18, 20) simple-cubic lattice with periodic boundary conditions and interact by way of a nearest neighbour coupling. The system undergoes a first order phase transition with a spontaneous order S = 0.333 ± 0.009 at the clearing temperature Tc given by βce = 0.894 ± 0.001, where e denotes the maximum interaction energy between two nearest neighbours. The pretransitional light scattering in the isotropic phase can be reasonably well described by [T - Tc∗]−1, with (Tc - Tc= 0.009 ± 0.007 for n = 14 and (Tc - Tc∗)/Tc = 0.007 ± 0.004 for n = 16. This type of divergence is in agreement with experiment.

First-principles prediction of the high-pressure phase transition and electronic structure of FeO: Implications for the chemistry of the lower mantle and core

Under shock-wave compression, Fe{sub 1{minus}x}O undergoes a transition to a dense metallic phase at pressure near 70 GPa. The geochemical significance of this transition has been unclear. Here, first-principles electronic structure calculations (using the FLAPW method and GGA exchange-correlation) show that the shock-wave discontinuity of FeO results from a RB1 (rhombohedrally distorted NaCl structure) to B8 (NiAs structure) transition. The metallic nature of the FeO (B8) phase is argued to result from a breakdown of the Mott insulating condition, rather than an Fe(3d)-O(2p) gap closure. As such, the metallization of FeO is probably not a basis for invoking oxygen in the Earth`s core. The stability of FeO(B8) over FeO(RB1) at high pressure is comparable to the ideal {minus}T{Delta}S of mixing of FeO in (Mg, Fe)O at mantle temperatures. Consequently, it is uncertain if FeO(B8) is present as a separate phase in the Earth`s interior. 27 refs., 5 figs., 1 tab.

Origin of orbital momentum and magnetic anisotropy in transition metals

Orbital angular momentum is necessary in order to have magnetic anisotropy. In a magnetic system, orbital angular momentum is caused by spin‐orbit coupling as well as by many‐body correlation effects. Standard band‐structure calculations only include the first of these two contributions. In this paper it is argued that, even in transition metals, the second contribution is probably more important.

Electronic and structural properties of rare earth metals at normal and high pressures: Eu and Yb

Abstract Ground state properties of the divalent rare earth metals Eu and Yb at ambient and high pressures are investigated by calculating their band structures and total energies using the linearized muffin-tin orbital method. To monitor the strengths of the 4f interactions in the local density approximation the hybridization of the 4f electrons is either fully included (itinerant model) or completely neglected (localized model). The effects of spin-polarization are also included for Eu. Divalent to trivalent valence transitions under pressure are discussed and compared with recent X-ray absorption experiments. For Yb, the structural stability of its fcc, bcc and hcp phases is investigated and results are presented.

Antiferromagnetism in face‐centered‐tetragonal iron

The total energy of face‐centered‐tetragonal iron is calculated within density‐ functional theory. We have obtained results for nonmagnetic, ferromagnetic, and antiferromagnetic iron. In the range of tetragonal structures we have studied, our total‐ energy calculations for the ferromagnetic phase give just two minima: One is nearly bcc (c/a=0.71) and one is nearly fcc (c/a=1). The antiferromagnetic phase yields only one minimum near the fcc structure, but is unstable near the bcc structure. The global minimum in total energy is antiferromagnetic. The difference in total energy between ferromagnetic and antiferromagnetic iron shows an oscillatory behavior as a function of c/a. Our results show that it might be possible to grow iron films with a large in‐plane lattice constant that have an antiferromagnetic ordering.

Total energy calculations for ZrO2

Abstract Total energy calculations are presented for zirconia in its tetragonal and cubic structure. The results show that the phase transition from tetragonal to cubic is driven by the thermal motion of the oxygen atoms. The theoretical value of the cohesive energy is in good agreement with experiment. The electric field gradients are in agreement with the experimental values obtained from Perturbed Angular Correlation measurements. This indicates that the lattice distortion around the probe tantalum nucleaus is small.

Electronic structure of LaN: Prediction of a small band overlap semi-metal☆

Abstract Results of a detailed theoretical investigation are reported which appear to resolve whether LaN is a semiconductor or a semi-metal. It is found that LaN has a band overlap of approximately 40 mRy making it a semimetal. A detailed analysis of the physical approximations and of the numerical precision indicate that this result has an uncertainty of ∼ 15 mRy which is too small to alter the conclusion.

Electronic structure of face‐centered tetragonal iron

Thin films of iron can be grown in either the bcc or fcc structure when using an appropriate substrate. Since the two lattices never match perfectly, it is to be expected that tetragonal distortions are present. Therefore, we have performed total energy calculations for face‐centered tetragonal iron in both the ferromagnetic and paramagnetic states. The standard bcc and fcc structures are two special cases of the face‐centered tetragonal space group. There are two minima in the total energy, one near the bcc line and one near the fcc line. The fcc minimum has the lowest total energy. Near the fcc minimum we find a region in the c‐vs‐a plane where our calculations have trouble converging. We associate this with the existence of a low‐spin metastable state in this region. We also study the values of the magnetic moments as a function of crystal structure.