Self-consistent APW Method Research Articles

A self-consistent relativistic APW method with the spin-orbit interaction treated as a perturbation

A simple method for including spin-orbit corrections in self-consistent relativistic APW band structure calculations is presented in which the spin-dependent part of the APW matrix is treated as a perturbation. The solution of the spin-independent problem is used in a way that requires little additional time or coding to include spin. The full calculational procedure is discussed and calculations of spin-orbit splitting in TaC are described to illustrate the method.

Fermi surface of LaAg

Electronic structure, especially the Fermi surface, is calculated for the intermetallic rare-earth compound LaAg, known to show the structural phase transition when In is substituted for Ag, by a self-consistent fully-relativistic APW method with the exchange-correlation potential in a local-density approximation. The Fermi surface is found to consist of large hole and electron sheets as well as small hole and electron sheets. This result confirms well the theoretical prediction by Niksch et al. (1987). These Fermi surface sheets are found to explain the experimental results for the de Haas-van Alphen effect by Niksch et al. (1987) and Motoki et al. (1995) reasonably well. But, the frequency branches originating from the large hole sheet have been observed only partially. Local curvature of the large hole sheet is investigated as a possible origin of the disappearance of these frequency branches.

Fermi Surface of LaRu2Ge2and CeRu2Ge2within Local-Density Band Theory

We derive the Fermi surface for LaRu 2 Ge 2 by a self-consistent relativistic APW method within the framework of a local-density approximation. The Fermi surfaces thus obtained are composed of four hole sheets and an electron sheet, all of which have no open orbits. The Fermi surface topology is consistent with the experimental results for the high-field transverse magnetoresistance. These Fermi surfaces explain reasonably well the absolute magnitude and the angular dependence of the de Haas-van Alphen (dHvA) frequency-branches. Moreover, we use the theoretical Fermi surface of LaRu 2 Ge 2 to re-examine an origin of the dHvA frequency-branches for a ferromagnetic CeRu 2 Ge 2 regarded as non-Kondo-lattice system.

Electronic band structures and unoccupied densities of states for Lu compounds

The band structures for Lu intermetallic compounds (LuPd 3, LuAl 3 and LuAl 2) and Lu and Sr pnictides (LuAs, Lu 4As 3 and Sr 4As 3) are calculated up to 14–20 eV above the Fermi level by a self-consistent APW method. The agreement between the calculated density of states curves and the observed BIS spectra is quite good for intermetallic compounds, although some discrepancies are found for pnictides.

Magnetic properties of pseudo-binary compounds Y(Fe,Al) 2 and Y(Co,Al) 2

The electronic structures of binary compounds YM 2 (M = Fe and Co) and ordered ternary compounds Y(M 0.75Al 0.25) 2 and Y(Fe 0.25Al 0.75) 2 with the cubic Laves phase structure are calculated by the self-consistent APW method. The anomalous magnetic properties observed in Y(Fe,Al) 2 and Y(Co,Al) 2 are discussed using the calculated results of the density-of-states curve.

Isomer shift and atomic environment effect in the intermetallic compound Y(Fe 1− xAl x) 2

The isomer shift of the Fe nucleus in the intermetallic compound Y(Fe 1− x Al x ) 2 with the C15-type Laves phase structure is discussed by calculating the charge density of the s electrons. The calculations are carried out by using the self-consistent APW method for YFe 2 and the ordered ternary compounds Y 2Fe 4 n Al n ( n = 1, 3). The calculated charge density of the 4s electrons at the Fe nucleus site is shown to decrease with increasing Al content, which is consistent with the observed isomer shift. The atomic environment effect on the isomer shift of a Fe nucleus surrounded by Al atoms is discussed.

Effect of the Spin-Orbit Interaction on the Fermi Surface of LaSn3

Electronic structure is calculated for LaSn 3 by a self-consistent relativistic APW method with the one-electron potential in the local-density approximation. LaSn 3 is a reference for the mixed-valence compound CeSn 3 in which the 4f electrons have recently been proven to be itinerant and contribute directly to the formation of the Fermi surface. Here, the relation between the Fermi surfaces of LaSn 3 and CeSn 3 is investigated. The main Fermi surface of LaSn 3 consists of a distorted hole sphere and a network with slender arms, both of which are connected with small necks. These sheets can explain the de Haas-van Alphen effect and the high-field magnetoresistance reasonably well. The distorted hole sphere in LaSn 3 and the hole sheet in CeSn 3 originate from the eighth band, and look similar to each other. In CeSn 3 , the electron sheet exists as a result of compensation.

The Fermi Surface of Itinerant 4f Electrons in CeNi

Based on the itinerant-electron model for the 4f electrons, the energy band structure and the Fermi surface is calculated for the mixed-valence cerium compound CeNi and its reference material LaNi by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. Both CeNi and LaNi are compensated metals, and their hole and electron Fermi surfaces are multiply-connected sheets with open orbits, the direction of which is consistent with the high-field magnetoresistance. Though they are quite different from each other, the Fermi surfaces for CeNi and LaNi can explain reasonably well both the magnitude and the angle dependence of the de Haas-van Alphen effect frequency branches. These theoretical results suggest that the 4f electrons may be itinerant in the ground state in CeNi, as they are in CeSn 3 .

Electronic Structure and Fermi Surface of UB12

Based on the itinerant-electron model for the 5f electrons, the energy band structure and the Fermi surface are calculated for the cubic uranium dodecaboride UB 12 , known to be a paramagnet having the electronic specific heat constant of 20 mJ/K 2 mole, by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. The energy band structure is that of a compensated metal having 0.32 holes/cell and the compensating number of electrons. Both the hole and the electron sheets of the Fermi surface are multiply-connected with open orbits, the direction of which is consistent with the high-field magnetoresistance. By these Fermi surfaces, both the magnitude and the angular dependence of the frequency branches of the de Haas-van Alphen effect observed recently by Ōnuki et al . can be explained reasonably well.

Electronic Band Structure of Th3Ni3Sb4and Th3X4(X=P, As, Sb)

In order to clarify the origin of the semiconductor like behavior of U 3 Ni 3 Sb 4 , one-electron energy band structures for the isostructural Th 3 Ni 3 Sb 4 and the Th 3 P 4 type Th 3 X 4 (X=P, As, Sb), which belong to the same space group, are calculated by the self-consistent APW method with the local density approximation. The calculated results for Th 3 X 4 show that the compounds are the narrow gap semiconductor or semimetal; the valence bands are derived from the X p states and the conduction bands from the Th 6 d states. Th 3 Ni 3 Sb 4 is also the semiconductor and the valence bands consist of the Ni 3 d and Sb 5 p states. Due to the mixing between the Ni 3 d and Th 6 d states, the empty Th 6 d conduction band is shifted up resulting a gap of 0.36 eV. This result explains reasonably why U 3 X 4 is semimetal but U 3 Ni 3 Sb 4 is semiconductor with a gap of 0.2 eV.

Electronic structure and metal-nonmetal transition in liquid Cs?Sb and Cs?I systems

The electronic structures of liquid Cs−Sb and liquid Cs−I systems have been calculated using the self-consistent semirelativistic APW method within the superlattive model. We have investigated the nature of chemical bonding in connection with the composition dependent metal-nonmetal transition in these systems. It is found that Cs−Sb system is principally ionic as well as Cs−I system, but appreciable admixture of the metallic bonding is observed; this explains the different behavior between the two systems in their composition-induced metal-nonmetal transitions.

Electronic Band Structure of YbInCu4and LuInCu4

One-electron energy band structure for LuInCu 4 , which is a proper reference material for the study of the valence transition in YbInCu 4 , is calculated by a self-consistent APW method with the local density approximation. The calculated result shows that the compound is the semimetal. This property is consistent with the observed unusual behavior. In order to estimate the mixing term between the 4 f electron and the valence and conduction electrons, the energy band structure for YbInCu 4 is also calculated. The obtained result is followings; ( p f σ)=0.27 eV for Yb 4 f and Cu p states and ( d f σ)=-0.14 eV for Lu 4 f and Cu 3 d states. These values are nearly same order as those of Ce compounds.

Fermi surface oF CeSn3

Based on an itinerant model for the 4f electrons, the energy band structure is calculated for CeSn3, known to be the heavy-electron system having the Kondo temperature of about 200 K, by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. Large hole and electron sheets of the Fermi surface clarify origins of all of the major frequency branches of the order 107 Oe of the de Haas-van Alphen effect for the field directions on both {100}and {110} planes.

Fermi surface of CeSn3

Based on an itinerant model for the 4f electrons, the energy band structure is calculated for CeSn3, known to be the heavy-electron system having the Kondo temperature of about 200 K, by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. Large hole and electron sheets of the Fermi surface clarify origins of all of the major frequency branches of the order 107 Oe of the de Haas-van Alphen effect for the field directions on both {100}and {110} planes.

Electronic Structure of CeSn3

Based on an itinerant-electron model for the 4f electrons, the energy band structure is calculated for CeSn 3 , known to be the heavy-electron system having the Kondo temperature of about 200 K, by a self-consistent relativistic APW method with the exchange and correlation potential in the local-density approximation. An itinerant-electron model assures that this compound is a compensated metal. The large, nearly spherical hole sheet of the Fermi surface explains one of the major frequency branches of the de Haas-van Alphen effect of the order 10 7 Oe. The electron sheet is essentially spherical but highly distorted by the strong 4f-Sn 5p hybridization. It explains clearly origins of all other major frequency branches. These results support the view that the 4f electrons in the heavy-electron Ce compounds should be treated by an itinerant-electron picture.

Nature of Doped Electrons in Nd2-xCexCuO4: Electronic Band Structures of Nd2CuO4Type M2CuO4(M=La, Ce and Th)

One-electron energy band structures for La 2 CuO 4 , Ce 2 CuO 4 and Th 2 CuO 4 with the Nd 2 CuO 4 type crystal structure were calculated by the self-consistent APW method with the local density approximation. The bonding-antibonding splitting between the Cu 3 d ( x 2 - y 2 ) and O 2 p states on the CuO 2 plane makes a pair of sub-bands. In La 2 CuO 4 , the Fermi energy cuts the middle of antibonding band resulting in the half-filled band. By replacing La with tetravalent Th, the Cu 3 d states raise due to the increase in the number of Cu 3 d electron but the bonding band made from Th 6 d (3 z 2 - r 2 ) state falls down. In Ce 2 CuO 4 , the Fermi energy cuts the bottom of 4 f bands. To raise the 4f states, a correction is introduced to the Ce potential and then Ce becomes nearly tetravalent resulting in similar band structure to that of Th 2 CuO 4 . By considering the strong correlation in the Cu 3 d ( x 2 - y 2 ) state, the doped electrons in Nd 2- x M x CuO 4 (M=Ce, Th) are thought to be injected into t...

Electronic band structure of ThNiSn

One-electron energy band structure for ThNiSn, which is a proper reference material for the study of the anomalous physical properties of UNiSn, is calculated by a self-consistent APW method with the local density approximation. To clarify the feature of band structure, the band calculation is performed for the isostructural ThRhSb and the NaCl type ThSb, too. The valence bands consist of the Sn 5p and Ni 3d states. Due to the strong mixing of Sn 5p and Ni 3d states, the bonding and anti-bonding bands are formed and the non-bonding Ni 3d bands locate between them. The conduction bands are derived from the Th 6d states and are raised by the mixing of Th 6d and Ni 3d states. A band gap appears between the occupied valence bands and the empty conduction bands. The mechanism of anomalous properties of UNiSn is considered.

Fermi Surface of ThC and UC

With a symmetrized, self-consistent relativistic APW method, the electronic structure is calculated for UC by using the exchange and correlation potential in the local-density approximation. It is predicted that UC is a semimetal which has 0.068 holes/cell and the compensating number of electrons. The Fermi surface consists of the three hole pockets in the C 2p valence band which are centered at the X points and six electron pockets in the U 5f conduction band which are centered at the W points. These hole and electron sheets can explain reasonably well the angular dependence of frequencies of the de Haas-van Alphen effect which have recently been measured for UC. For reference, the electronic structure is calculated for ThC also.

Isomer shift of Fe in the intermetallic compound Y(Fe 1− xAl x) 2 with C15-type Laves phase structure

The isomer shift of Fe nucleus in intermetallic compound Y(Fe 1− x Al x ) 2 with the C15-type Laves phase structure is discussed by calculating the charge density of s electrons in the local density approximation and the self-consistent APW method. The calculated charge density of the 4selectrons at the Fe nucleus position is shown to decrease with increasing Al content, which is consistent with the observed isomer shift. The atomic environment effect on isomer shift of the Fe nucleus surrounded by the Al atoms are discussed.

Electronic band structure of paramagnetic and antiferromagnetic La 2NiO 4

One-electron energy band structures for paramagnetic and antiferromagnetic La 2NiO 4, which is one of the isomorphous compound of high T c superconducting La 2−xM xCuO 4, have been calculated by the self-consistent APW method. The paramagnetic state with the tetragonal structure is metallic. Within the conventional local spin density approximation, the antiferromagnetic ground state is found to be unstable. The stable antiferromagnetic state with the sublattice magnetization of 1.0 μ B/Ni is obtained by using the exchange interaction enhanced by 50 %.