the entanglement at zero-temperature is studied in a two-qubit xz spin-1/2 chain model in anexternal magnetic field which is applied in the z direction. we have obtained an analytical relation forthe effect of the external magnetic field on the concurrence. it is shown that the ground state of thesystem depends on the strength of exchange coupling. we have shown that the analytical relation oft...

The entanglement at zero-temperature is studied in a two-qubit XZ spin-1/2 chain model in anexternal magnetic field which is applied in the z direction. We have obtained an analytical relation forthe effect of the external magnetic field on the concurrence. It is shown that the ground state of thesystem depends on the strength of exchange coupling. We have shown that the analytical relation oft...

in this paper we studied the thermal negativity in a two-qubit xx spin ½ chain model and xxx spin1/2 chain model(isotropic heisenberg model)spin-1/2 chain subjected to an external magnetic field inz direction. we calculate analytical relation for the thermal negativity for two qubit xx and xxx spinchain models in the external magnetic field. effects of the magnetic field and temperature on then...

We calculate the conductance as a function of temperature G(T) through Au monatomic chains containing one Co atom as a magnetic impurity, and connected to two conducting leads with a fourfold symmetry axis. Using the information derived from ab initio calculations, we construct an effective model Ĥ(eff) that hybridizes a 3d(7) quadruplet at the Co site with two 3d(8) triplets through the hoppin...

In this paper we studied the thermal negativity in a two-qubit XX spin ½ chain model and XXX spin1/2 chain model(isotropic Heisenberg model)spin-1/2 chain subjected to an external magnetic field inz direction. We calculate analytical relation for the thermal negativity for two qubit XX and XXX spinchain models in the external magnetic field. Effects of the magnetic field and temperature on then...

Problems of strongly interacting electrons can be greatly simplified by reducing them to effective quantum spin models. The initial step is renormalization of the Hamiltonian into a lower energy subspace. The positive and negative U Hubbard models are explicitly transformed into the Heisenberg and -x-xz models respectively. Basic tools of quantum magnetism are introduced and used: spin coherent...

We report the results of a series of density functional theory (DFT) calculations aimed at predicting the (57)Fe Mössbauer electric field gradient (EFG) tensors (quadrupole splittings and asymmetry parameters) and their orientations in S = 0, (1)/(2), 1, (3)/(2), 2, and (5)/(2) metalloproteins and/or model systems. Excellent results were found by using a Wachter's all electron basis set for iro...

For the antiferromagnetic, highly anisotropic XZ and XXZ quantum spin chains, we impose periodic boundary conditions on chains with an odd number of sites to force an interface (or kink) into the chain. We prove that the energy of the interface depends on the momentum of the state. This shows that at zero temperature the interface in such chains is not stable. This is in contrast to the ferroma...

The paper presents exact calculations of thermodynamic quantities for the spin2 isotropic XY chain with random lorentzian intersite interaction and transverse field that depends linearly on the surrounding intersite interactions. PACS codes: 75.10.-b

High-valent transition-metal-substituted Keggin-type polyoxometalates (POMs) are active and robust oxidation catalyst. The important oxidized intermediates of these POM complexes are very difficult to be characterized by using the experimental method, and thus no detail information is available on such species. In the present paper, density functional theory (DFT) calculations have been carried...