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Electronic band structure calculations were performed on the nonmagnetc (NM) and antiferromagnetic (AFM) phases of LiFeX (X = P, As and Sb) compounds using ab initio method. The crystal structure of these compounds is well tetragonal P4/nmm structure (space group = 129). Self-consistent calculations were performed by planewave pseudo-potential, density functional based method using PWSCF-Quantum Espresso code. To study the electronic structure and magnetic ordering, the total energies of these compounds have been computed as a function of reduced volumes and fitted with Brich Murnaghan equation. The estimated lattice parameters are in good agreement with available experimental data. The calculated Fe magnetic moment for LiFeSb is larger than LiFeAs and LiFeP. The obtained electron–phonon coupling constant (λ) for the NM phase are very weak when compared to that of AFM phase of LiFeX compounds. Present calculations reveal that the electron–phonon coupling constant λ decreases as a function of pressure.

The development of ferroelectric photovoltaic (FE-PV) materials has been limited for a long time due to their large bandgap. Many strategies for lowering the bandgap have been suggested to promote FE-PV properties. The effects of magnetic ordering and B-site-cation ordering to lower the bandgap of FE-PV are investigated in this paper using first-principles calculations. Results show that the most stable structure of tetragonal Bi₂FeCrO₆ ($t$-Bi₂${\text{FeCrO}}_6)$ is the AS1 structure (Fe/Cr alternate stacking ordering) with C-type antiferromagnetic ordering (defined as AC-$t$-Bi₂FeCrO₆), which has a small bandgap, suggesting that AC-$t$-Bi₂FeCrO₆ is among the FE-PV materials with the highest application potential.

Raman spectra of Ho${}_{1-x}$Nd_xFe(BO₃)₄ ($x=1$, 0.75, 0.5, 0.25) have been studied in temperature range 10–400K. Two compositions ($x=1$, $x=0.75$) demonstrate structural phase transition with soft mode restoration. The addition of Nd atoms increases interatomic spacing and decreases the temperature of structural phase transition. The solid solutions ($x=0.75$, 0.5, 0.25) demonstrate the emergence of the peaks corresponding to magnetoelastic interaction below Néel temperature. The order parameter of the magnetic phase transition has been determined. The equal concentrations of holmium and neodymium atoms prevent magnon soft modes condensation caused by exchange interactions in Fe–O–Fe chains are observed. Calculations confirm the data obtained in the experiment.

In this paper, detailed examination of the doping effect on electronic band structure, magnetic properties of nonmagnetic (NM) and striped antiferromagnetic (S-AFM) phases of MFeAs(M = Li, Na) compounds were carried out using ab initio method. The crystal structure of these compounds is a well known tetragonal structure. Self-consistent calculations were performed by plane wave pseudo potential, density functional based method using PWSCF-Quantum Espresso code. To study the structural phase stability, the total energies of these compounds were calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. 3d valence elements like Mn, Co induce strong local magnetic moments on doping. However, Cu substitution weakens the average local moments. The 3d elements on doping at Fe site directly affect the electrons correlations in the Fe–As layer.

We demonstrate the potential of the electronic-structure methods developed recently for the calculation of optical properties of solids. The many-body effects, i.e. quasiparticles, excitons and local fields, are fully taken into account by solution of the combined Dyson and Bethe-Salpeter equations. The principal effects but also the validity of the used approximations are discussed for bulk semiconductors such as Si and prototypical molecules such as SiH₄. The extension of the theory to systems with spin ordering or strong confinement is demonstrated. Their influence on the many-body effects is discussed for the paradigmatic insulator MnO and a silicon nanocrystal.