Phonon-induced superexchange

The superexchange in V2+ --- O2− --- V2+ pair in MgO is calculated including the orbit-lattice interaction into theone-electron. hamiltonian. Although the exchange by itself is ferromagnetic, the phonon-induced contribution is found to be dominantly antiferromagnetic

Line width in magnetic resonance due to emission of radiation

Line width in ferromagnetic resonance is found to consist of the magnon scattering, the superradiance, and a new effect due to the simultaneous presence of magnon scattering and the superradiance

Band structure and density of states in the normal state of FeSe, Fe2Se2, Fe2Se1 and Fe2SeTe superconductors

We have calculated the band structure of FeSe. FeSe from which 2 atoms of Se out of 4 per unit cell have been removed and a system in which 2 Te atoms have been substituted for 2 Se atoms in a unit cell in the normal state. In all of the cases the Fermi energies cross multiple bands and there is always at least one conduction band minimum whose energy is lower than the valence band maximum. Hence, on the basis of the calculated band structures, these systems have no semiconducting band gap and should behave as metals. Similarly, there is non-vanishing density of states at the Fermi level. Large effects are found in the density of states. The normal state gap reduces in the composition which becomes superconducting. (C) 2010 Elsevier B.V. All rights reserved

Ab initio calculations of vibrational frequencies in a glassy state of selenium

We used the density functional theory to calculate the vibrational frequencies of clusters of atoms. We obtained the bond distances and angles for which the energy of the Schrodinger equation is minimum. We found the bond distance between two Se atoms to be 232.1 pm when double zeta wave function was used. The frequency of oscillations was calculated to be 325.3 cm(-1) but the intensity was zero because Se(2) molecules were present in a very small number. When polarised double zeta wave function (DZP) was used, the bond length of Se(2) was found to be 223.1 pm and the frequency is 367.4 cm(-1). Similarly for other clusters of selenium, we calculated the frequencies and compared with the experimental data. The experimental Raman spectra give 250 cm(-1) for a selenium glass. By comparing the experimental frequencies with those calculated we found that linear Se(3) was present in the glass. This indicates the possibility of linear growth in the glass

DFT calculations of vibrational frequencies of carbon-nitrogen clusters: Raman spectra of carbon nitrides

We have performed the calculation of structures of clusters containing carbon and nitrogen atoms. We determine the bond lengths in each case. We also calculate the vibrational frequencies of all of the clusters. We compare the calculated values of the vibrational frequencies with those measured by the Raman spectra of amorphous carbon nitrides. Some of the calculated frequencies are in agreement with those measured. We identity that linear structures and hence ``back bones'' are present in the glassy state

Ab initio calculation of vibrational frequencies of AsO glass

We have used the density-functional theory to make models containing arsenic and oxygen atoms. The structures are optimized for the minimum energy of the Schrodinger equation. In this way, we obtain the bond distances and angles of the stable structures. We obtain the vibrational frequencies of each cluster. The calculated vibrational frequencies are compared with those found in the experimental Raman spectra. The values of the vibrational frequencies calculated for AsO(2:)ASO(4)(T(d))(:)AsO(2) (rectangular), AsO(2) (triangular) and AsO(3) (pyramidal) agree with those found in the Raman spectra of vitreous aresenic oxide, indicating that these clusters are really present in the arsenic oxide glass. (C) 2009 Elsevier B.V. All rights reserved