Plane-wave Self-consistent Field Research Articles

The Structural Stabilities and Electronic Properties of Orthorhombic and Rhombohedral LaCrO<sub>3</sub> — A First-Principles Study

The equilibrium structures of orthorhombic LaCrO3 (O-LaCrO3) and rhombohedral LaCrO3 (R-LaCrO3) crystals were investigated by using the plane-wave self consistent field (PWSCF) method based on density functional theory (DFT). The optimized lattice parameters for both phases are in accordance with experimental results reported in literature, confirming the reliability of LSDA+U scheme used in the calculations. We have quantificationally investigated the binding energies and electronic properties of these two types of LaCrO3 crystals. The negative total energy and binding energies indicate the ground state property and the good structrual stability of O-LaCrO3 crystal, which is important for the preparation of nano materials, the synthesis of ceramic materials made of doped O-LaCrO3 crytals, as well as their applications in high technology fields, and predict the metastable property of R-LaCrO3 crystal. Furthermore, the band structures show that O-LaCrO3 is a direct semiconductor with wide energy gap, while R-LaCrO3 is an indirect semiconductor with narrow energy gap. The interaction between Cr and O atoms in O-LaCrO3 crystal possesses the character of covalent bonding.

Investigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn2V Ga

The band structure calculation for the compound Mn2VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300 K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6 K yields magnetic moment values of 1.28 μB and −0.7 μB for Mn and V, respectively, confirming the ferrimagnetic ordering.

First-Principles Study of the Influence of (110) Strain on the Ferroelectric Trends of TiO2

We investigate the impact of uniaxial strain on atomic shifts, dipolar interactions, polarization and electric permittivity in TiO2 (rutile) by using two different implementations of density functional theory. It is shown that calculations using the Vienna ab inito simulation package (VASP) and the plane-wave self-consistent field method (PWscf) yield qualitatively the same atomic relaxations and ferroelectric trends under strain. The phonon dispersion curves of unstrained and strained TiO2 (rutile) obtained by employing the linear response method confirm previous calculations of the giant LO-TO splitting and the appearance of soft polar modes. A second order phase transition into a ferroelectric phase with polarization along (110) appears under expansive strain in (110) direction.

First-Principles Calculation and Experimental Investigations on Full-Heusler Alloy Co$_{2}$FeGe

First-principles calculation has been carried out for the full Heusler alloy Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeGe within the scheme of density functional theory using plane-wave self-consistent field method. The spin polarized band structure does not show any energy gap at the Fermi level for both up and down spin electrons. Atom resolved magnetic moment on each site was observed to be 1.3 mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> (Co), 2.9 mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> (Fe), and 0.0 mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> (Ge). X-ray diffraction studies reveal a B2-type structure for the bulk sample and cubic L2 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> structure for the melt-spun ribbons. The lattice parameter value for the ribbon is 5.736 Aring, and its Curie temperature is around 981 K. The magnetic moment per formula unit at 5 K was observed to be 5.74 mu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> . The low temperature data ( < 100 K) follows the relationrho = rho <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> + AT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> + BT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.5</sup> , indicating the presence of one magnon spin-flip scattering.

Magnetic states for V(001) bcc surface: An ab initio study

Recent magneto-optical kerr effect and low energy electron diffraction experiments on V(001) surface probed the existence of surface magnetism. Following these experiments the authors performed an ab initio study for the magnetic states of V(001) surface using a plane wave self-consistent field code. The generalized gradient approximation is used to treat the exchange correlation potential. Structural optimization is considered for the systems. The results obtained from the study of V(001) bcc surface show metastable magnetic states with an energy difference, with respect to the ground state, less than 10meV/atom.

Electronic phase transition and amorphization inAuIn2at high pressure

High-resolution angular-dispersive x-ray diffraction shows that the intermetallic compound AuIn 2 retains its initial CaF 2 structure to pressures of 23 GPa. We observe continuous broadening of diffraction lines with pressure, leading to amorphization at 24 GPa. The pressure-volume equation of state exhibits an anomaly around 2.7 GPa, in agreement with previous findings and not attributable to nonhydrostaticity. Instead, ab initio plane-wave self-consistent field calculations indicate that the observed anomaly is associated with topological changes in the electronic band structure under pressure.