FP LAPW Research Articles

Study of Elastic Properies of Ti<sub>3</sub>Al Intermetallic Compound Using the <i>Ab Initio</i> Calculation

The elastic properties of a Ti3Al intermetallic compound were studied using full potential (FP LAPW ) with the APW+lo method. The FP-LAPW is among the most accurate band structure calculations currently available and is based on the density functional theory with general gradient approximation for the exchange and correlation potential. This method provides the structural properties of the ground state as bulk modulus, equilibrium lattice parameter, and equilibrium minimum energy, and the elastic properties as shear modulus, young modulus, Zener coefficient (anisotropy), and Poisson coefficient. The calculated elastic properties are coherent with the elastic properties of the material.

Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations

Borate minerals composed of [Bφ 3 ] triangles and/or [Bφ 4 ] tetrahedra (φ = O or OH) commonly exhibit complex polymerizations to form diverse polyanion groups. High-resolution solid-state magic angle spinning (MAS) 11 B and 25 Mg NMR spectroscopy at moderate to ultrahigh magnetic fields (9.4, 14.1, and 21.1 T) allows for very accurate NMR parameters to be obtained for the borate dimorphs, inderite, and kurnakovite, [MgB 3 O 3 (OH) 5 ·5H 2 O]. Improved agreement between experimental results and ab initio density functional theory (DFT) calculations using Full Potential Linear Augmented Plane Wave (FP LAPW) with WIEN2k validates the geometry optimization procedures for these minerals and permits refinements of the hydrogen positions relative to previous X-ray diffraction crystal structures. In particular, the optimized structures lead to significant improvements in the positions of the H atoms, suggesting that H atoms have significant effects on the 11 B and 25 Mg NMR parameters in inderite and kurnakovite. This study shows that combined high-resolution NMR spectroscopy and ab initio theoretical modeling provides an alternative method for the refinement of crystal structures, especially H positions.

Study of energy bands and magnetic properties of Co2CrSi Heusler alloy

The electronic and magnetic properties of Co2CrSi is calculated by using full-potential linearized augmented plane wave (FP–LAPW) method based on density functional theory (DFT). Density of states (DOS), magnetic moment and band structures of the system are presented. For the exchange and correlation energy, local spin density approximation (LSDA+U) with the inclusion of Hubbard potential U is used. Our calculation shows indirect bandgap of 0·91 eV in the minority channel of DOS. This is supported by band structures and hence favoured the half metallic ferromagnetic (HMF) nature of the system. The effective magnetic moment of 4·006 μB also supported our conclusion with a near integral value. The DOS of Co and Cr were found to hybridize and was also responsible for the ferromagnetic nature of the system.

Lattice Dynamics of Ferroelectric SbSBr Crystal

The temperature dependence of phonon dispersion, total and partial phonon DOS of SbSBr crystal have been determined in paraelectric phase at T = 30 K and in ferroelectric phase at T = 11 K using FP—LAPW method in the framework of DFT along with the GGA approximation. Temperature dependence of total and partial phonon DOS for Sb, S and Br atoms where used for calculation of the vibration free energy of the unit cell Fvib and contribution from Sb, S and Br atoms to the free energy Fi,μ along c(z) —axis in quasiharmonic approximation in paraelectric and ferroelectric phases in temperature range from 11 K to 294 K. For investigation of softening effect nature of phonons along c(z) —axis the mean-squared displacements of Sb, S and Br atoms in x -, y -, z - direction have been calculated in quasiharmonic approximation in ferroelectric and paraelectric phases.

Ab initio study of electronic, magnetic and optical properties of CuWO4 tungstate

Ab initio calculations based on the density-functional theory have been employed to study the electronic and magnetic properties of copper tungstate CuWO4, as well as its optical characteristics in the ultraviolet region, up to 40eV. The electronic structure around the band gap is dominated by the O p- and the Cu d-states and it is quite different from the recent spin-restricted calculations of the same compound. The most stable antiferromagnetic state and the values of magnetic moments at Cu sites and O(3) oxygen atomic sites (closest to Cu2+ ions in zigzag antiferromagnetic chains) are in agreement with experiments. The gap is found to be indirect with the acceptable value only after use of the LDA+U rotationally invariant self-consistent full potential linearized augmented plane wave (FP LAPW) approach. The optical spectra are analyzed, compared, and interpreted in terms of calculated band structures. It is shown that absorption process involves significant energy flow from the O ions to the Cu ions.

Theoretical studies of thermal decomposition of anhydrous cadmium and silver oxalates

Detailed analysis of the results of full potential linearized augmented plane wave (FP LAPW) ab initio calculations for anhydrous silver and cadmium oxalates, reported in first part of this paper [1] has been presented. Additional calculations of Bader’s AIM (Atoms in Molecules) topological properties of the electron density, bond orders (Pauling, Bader, Cioslowski and Mixon) and bond valences according to bond valence model have been done. The obtained results show the similarities in electronic structure of both compounds and support the conclusion, that during the thermal decomposition process, these compounds should most probably decompose to metal and carbon dioxide, in agreement with the experiment.

First principles studies of thermal decomposition of anhydrous zinc oxalate

The results of first principles calculations of band structure, density of states and electron density topology of ZnC2O4 crystal are presented. The calculations have been performed with WIEN2k FP LAPW ab initio package. The obtained SCF electron density has been used in calculations of Bader’s QTAIM (quantum theory of atoms in molecules) topological properties of the electron density in crystal. Additional calculations of bond orders (Pauling, Bader, Cioslowski and Mixon) and bond valences according to bond valence model have been done. The obtained results are analyzed from the point of view of the thermal decomposition process, and this analysis indicates, that most probably this compound should decompose to metal oxide, carbon oxide and carbon dioxide, in agreement with the experiment.

Electronic structure and optical properties of lead chloride

Spectra for the sets of optical functions for lead chloride are obtained for polarizations E ‖ a and E ‖ b at 10 K in the range of 4 to 30 eV. The calculations are carried out using synchrotron reflectivity spectra and a software package. The main features of the spectra of optical functions were established; they include the energies for volume and surface plasmons of two types. The bands and the spectra of permittivity and other optical functions for lead chloride crystals are calculated using the FP LAPW method. There was good agreement between the theoretical calculations and the data of the experimental spectra of R and other optical functions calculated using these R spectra.

Theoretical studies of thermal decomposition of anhydrous cadmium and silver oxalates

The results of first principles calculations of band structure, density of states and electron density topology of CdC2O4 and Ag2C2O4 crystals are presented. The calculations have been performed with WIEN2k ab initio program, using highly precise full potential linearized augmented plane wave (FP LAPW) method within Density Functional Theory formalism. The obtained SCF electron density has been used in calculations of Bader’s AIM (atoms in molecules) topological properties of the electron density in crystal. The obtained results show important similarities in electronic structure and electron density topology of both compounds and allow supposing, that during the thermal decomposition process these compounds should behave similarly, which is in agreement with the experiment.

X-ray spectra and electronic structures of the iron arsenide superconductorsRFeAsO1−xFx(R=La,Sm)

The electronic structures of undoped and fluorine-doped LaFeAsO superconductors and fluorine-doped SmFeAsO superconductors are studied using soft x-ray absorption and emission spectroscopy combined with full potential linearized augmented planes waves (FP LAPW) calculations. The comparison between the numerical simulations and the experimental $\text{Fe}\text{ }L$-emission spectra shows that the Fe states are concentrated near ${E}_{F}$, suggesting that the materials are not highly correlated systems. The comparison of the O $K$-edge and $\text{F}\text{ }K$-edge spectra with the calculated density of states shows that the F dopants do not directly participate in the electronic structure near ${E}_{F}$, and so they serve the same purpose as an oxygen vacancy leading to an increase in the number of available charge carriers. Increasing the amount of fluorine doped into the structure of SmFeAsO is shown to cause a narrowing of the bandwidth of occupied O valence states.

First-Principles Study on the Electronic Structure and Elastic Properties of YCu, DyCu and YAg

The electronic structure and elastic properties of YCu, YAg, and DyCu were studied by full-potential linearized augmented plane wave method (FP LAPW) on the basis of the density functional theory (DFT). The generalized gradient approximation (GGA) is applied for YCu, YAg, and the LDA+U is applied for DyCu. The density of states at the Fermi energy, NðEFÞ, are 1.08, 1.09, and 1.04 states/(eV unit cell) for YCu, YAg and DyCu, respectively. The elastic constants were calculated. The values for Pugh’s criterion are 2.30, 2.05 and 3.00 for YCu, DyCu and YAg, respectively. All of them are larger than 1.75, indicating the ductile manner of these materials. The calculated value of the anisotropy is close to 1, indicating highly isotropic behavior. [doi:10.2320/matertrans.MB200816]

Ideal Tensile Strength of Ni<sub>3</sub>Al and Fe<sub>3</sub>Al with D0<sub>3</sub> Structure

The ideal tensile strength along the [111] direction in the Fe3Al and Ni3Al intermetallic compounds with the D03 structure has been calculated from the first principles using the fullpotential linearized augmented plane-wave method (FP LAPW) within the density functional theory (DFT). The strains corresponding to the maximum sustainable stresses in both materials were determined and compared. The behavior of atomic magnetic moments as a function of strain was analyzed. The tensile test simulations have been theoretically simulated employing both the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchangecorrelation potential.

Features of hydrogen interaction in the Pd-based alloys with 3d transition metals

The effect of an alloying metal and its magnetic state on the hydrogen absorption energy has been investigated in the Pd-based alloys Pd(3)Me with 3d transition metals (Me = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) using calculations from first principles. The full-potential and linearly augmented plane wave (FP LAPW) method has been used in the local density approximation (LDA) for the exchange-correlation potential in the framework of the density functional theory (DFT). It has been found that the hydrogen solubility in an alloy increases if the centers of mass of s and d metal bands and s hydrogen band shift strongly toward the Fermi level. The changes in properties of hydrogen absorption as a function of its position in a crystal lattice structure and magnetic state of an alloy have been analyzed.

27Al and 23Na NMR spectroscopy and structural modeling of aluminofluoride minerals

Simulations of high-resolution 19F-decoupled 27Al and 23Na magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of the aluminofluoride minerals, cryolite, cryolithionite, thomsenolite, weberite, chiolite, prosopite, and ralstonite combined with theoretical modeling have given accurate values of chemical shift (δiso), and quadrupolar interaction parameters (Cq and η), thereby eliminating ambiguities incurred by the complex nuclear interactions. These NMR data have been correlated with local electronic environments in the minerals, which were calculated using Full Potential Linearized Augmented Plane Wave (FP LAPW) modeling based on the structures from X-ray diffraction (XRD) data. This combination of NMR, XRD, and modeling techniques allowed the analysis and optimization of the crystal structures.

The magnetic behavior and electronic structure of manganese (II)-azido complex [Mn(L) 2(N3) 2] n studied by first-principle calculation

Manganese (II)-azido complex [Mn(L) 2(N3) 2] n ( L = 4 -cyanopyridine) has been studied with the self-consistent full-potential linearized augmented plane wave method (FP–LAPW) based on the density functional theory (DFT). Spin distributions in ferromagnetic and antiferromagnetic states of it have been obtained by the calculation. The result shows that magnetic coupling through azido groups should be attributed to the spin delocalization effect.

The spin-density waves in thin films of Cr in the Fe/Cr/Sn/Cr multilayers

Magnetism of Fe/Cr/Sn/Cr multilayers have been studied by the first-principles density-functional theory. Calculations by the full-potential linearized augmented plane waves (FP LAPW) and screened Korringa–Kohn–Rostoker (SKKR) methods have shown that two types of solutions may be found in these systems: a high-spin (HS) and a low-spin (LS) ones in accordance with the Cr magnetic moment magnitudes. In this work, we have concentrated our attention on the LS solution. The calculation has shown that the LS solution has a phase slip of antiferromagnetic ordering in Cr and is classified as an incommensurate spin density wave (ISDW). The dependence of the ISDW solution on the thickness of Cr, lattice parameter and boundary conditions has been investigated.

From the Molecular Picture to the Band Structure of Cubic and Tetragonal Barium Titanate

A band structure of barium titanate crystal has been calculated with the WIEN2k program, using FP LAPW method. A broad dispersion of the valence band (about 5 eV) and a narrow forbidden energy gap (about 2 eV) confirm the crucial role of covalent interactions in this compound. The calculations have been performed for cubic and tetragonal structures of the crystal, which have allowed to determine the changes in the electronic structure due to the ferroelectric phase transition. It is found that the transition between cubic and tetragonal structures does not change significantly either the bands widths or their positions in relation to the Fermi level. The main difference concerns the character of the bands and is clearly related to the oxygen electronic states. This indicates that the ferroelectric behavior of the material may be explained by the crucial role of the π bonds formed by the oxygen ions. The band structure obtained remains in direct relation to the molecular picture thus confirming ligand field theory.

Magnetism and hyperfine magnetic fields in Fe/Cr/Sn/Cr and Cr/Sn multilayers

Abstract The paper is devoted to the theoretical study of the magnetic moments and hyperfine fields in Fe/Cr/Sn/Cr and Cr/Sn multilayers. The calculations are conducted by the FP LAPW, ASA SKKR and FP SKKR methods. The results obtained are compared with the calculations of other authors and Mossbauer spectroscopy experiments.

The fcc - bcc structural transition: I. A band theoretical study for Li, K, Rb, Ca, Sr, and the transition metals Ti and V

Employing a high-precision band structure method (FP LAPW - full potential linearized augmented plane wave) we calculate the total energy variation along the tetragonal distortion path connecting the body centred cubic (bcc) and the face centred cubic (fcc) structures. The total energy along this Bain transformation is calculated, varying c/a and volume, providing a first-principles energy surface which has two minima as a function of c/a. These are shallow and occur for the sp metals at the two cubic structures, while Ti (V) has a minimum at fcc (bcc) but a saddle point (i.e. a minimum in volume and a maximum with respect to c/a) at the other cubic structure. These features can be analysed in terms of an interplay between the Madelung contribution and the band energies. Our total energy results allow us to calculate the elastic constants and and to study the influence of pressure on the phase stability. These energy surfaces will be used in part II of this paper to investigate finite-temperature effects by mapping them to a Landau - Ginzburg expansion.