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The algorithm to calculate the sets of symmetry sectors for virtual indices of U(1) symmetric matrix product states (MPS) is described. The principal differences between open (OBC) and periodic (PBC) boundary conditions are stressed, and the extension of PBC MPS algorithm to projected entangled pair states is outlined.
A systematic study of the magnetism, mechanical, and optical behaviors of Mg{sub 0.75}TM{sub 0.25}S/Se (TM = Fe, Co, Ni) ordered alloys was conducted using the full-potential linearized augmented plane wave plus local orbital method. The ferromagnetic (FM) and antiferromagnetic (AFM) ground state energy differences and enthalpy of formation scrutinized their dynamical stability in the FM state. The elastic parameters decided their mechanical stability, ductile behavior, and partial ionic and covalent characters. Moreover, the calculated band structures and density of states revealed the type and origin of magnetism in terms of exchange splitting energies and exchange constants. The Fe- and Ni-doped MgS/Se alloys exhibited half metallic ferromagnetic (HMF) characteristics, while the Co-doped MgS/Se alloy depicted ferromagnetic semiconducting characters. A reduction in the magnetic moments of the transition metals was observed compared with their free space value, which is due to strong p-d hybridization. Furthermore, the optical spectrum showed the maximum light absorbed in the visible and in the UV region of the electromagnetic spectrum, which makes them potential candidates for optoelectronic and spintronic device applications.
Theoretical investigations on rutile SnO{sub 2} doped with V and Cr were performed by using recently implemented Tran and Blaha’s modified Becke-Johnson exchange potential model (TB-mBJ) based on density functional theory. The electronic, magnetic, dielectric and optical properties of V and Cr-doped tin oxide have been calculated by full-potential linearized augmented plane wave method (FP-LAPW) by WIEN2k code. The present works demonstrate accurate prediction of band structures and properties using the TB-mBJ model. The calculated values of magnetic moment, dielectric constant and refractive index of doped and undoped compounds agree well with the experimental results. The TB-mBJ model is a direct method without using empirical corrections and hence, the furnished data are useful in material modelling for spintronics applications.
The structural, magnetic, electronic and optical properties of Terbium-based binaries (TbX) (X = N, O, S and Se) in two cubic structures NaCl and CsCl have been investigated. This study is carried out by Full-Potential linearized Muffin-Tin orbitals (FP-LMTO) method in the framework of the functional theory of density (DFT) implemented in the lmtart code. The presence of f-state electrons in these induced high-correlation materials led us to study these systems using local density approximation (LDA) for the paramagnetic state and spin local density approximation (LSDA) for the ferromagnetic state within two cubic structures. We have demonstrated that these binaries are stable in the ferromagnetic state in the cubic phase of NaCl, which allows us to deduce the magnetic moments of these components. From the electronic band structures and density states, we have concluded that TbX (X = N, O, S and Se) are metallic in the NaCl phase. The results obtained in this work show that the theoretical parameters of the ground state, structure of the bands, density of the states (DOS) and optical properties agree well with other available theoretical and experimental data.
In this work, the structural, electronic, magnetic, and optical properties of Mn{sub 2}ZrGa full-Heusler alloy were investigated by using density functional theory (DFT) calculations. It is found that the spin-up states have a metallic character, but the spin-down bands have a pseudo-gap at the Fermi level. The total spin magnetic moment of Mn{sub 2}ZrGa (per formula unit) is 3.00 µ{sub B} at an equilibrium lattice parameter of 6.15 Å. The calculations show that Mn{sub 2}ZrGa is a ferrimagnetic with 81% spin polarization at equilibrium lattice parameter. The effect of lattice parameter distortion on the magnetic properties and spin polarization is also studied. It is found that the total magnetic moment preserves its value for a lattice parameter range of 5.96–6.30 Å. The decreasing of the lattice parameter leads to improvement of spin polarization. The real and imaginary parts of dielectric function and hence the optical properties including energy absorption spectrum, reflectivity, and optical conductivity are also calculated. The value of plasma frequency for spin-up and down electrons is located at 1.78 and 0.74 eV, respectively.
Plane-wave pseudo-potential methods based on density functional theory are used to study the electronic structures, magnetic, and half-metallic properties of the equiatomic quaternary Heusler alloys NbVMnAl and NbFeCrAl. Calculated results reveal that NbVMnAl and NbFeCrAl alloys are newly designed half-metallic ferrimagnets with a total magnetic moment (M{sub t}) of 2 μ{sub B}. We found that the Slater-Pauling rule, i.e., the relationship between the M{sub t} and the total number of valence electrons (Z{sub t}) of these two alloys was different. For NbVMnAl alloy, it obeys the M{sub t} = |Z{sub t} − 18| rule. For NbFeCrAl, it satisfies the M{sub t} = |Z{sub t} − 24| rule. Also, we observed that the half-metallic band gap (HM-BG) of these two alloys was different. Namely, for one material (NbFeCrAl), it is located in the spin-up channel, and in the other (NbVMnAl), it is located in the spin-down channel. To explain these phenomena, in this work, the generalized electron-filling rule was investigated, and the origin of the HM-BG of NbVMnAl and NbFeCrAl was studied. We hope that our work may provide theoretical guidance in searching for Nb-based equiatomic quaternary Heusler half-metals in the future.
Half-Heusler alloys RuMnZ (Z = P, As ) are studied in the framework of Density Functional Theory (DFT). Structural, electronic, magnetic, and optical properties are calculated and analyzed using the WIEN2k simulation code. All the calculations are done using the full potential linearized augmented plane wave (FP-LAPW) method. Equilibrium lattice parameters are found to be in the range 5.5–5.6 Å. Band gaps of the compounds and density of states (DoS) analysis reveal that the minority spin-down states are semi-conducting while the majority spin-up states are conducting confirming the half-metallic nature of the compounds. Hence, at Fermi level, states are 100 % polarized. The value of the total magnetic moment is found to be 2, i.e., M{sub Tot} = 2μ{sub B}. Several optical properties, including dielectric function, reflectivity, refractive index, conductivity, and absorption coefficient are calculated as well. It is revealed from the imaginary part of the dielectric function that the compounds are optically metallic.
The structural, elastic, and electronic properties of rare earth intermetallic R{sub 2}Ni{sub 2}Pb (where R = Ho, Lu, and Sm) compounds were investigated with the density functional theory (DFT) calculations. The calculations are performed using the full potential-linearized augmented plane wave (FP-LAPW) method within the framework of local density approximation (LDA). The calculated values of the equilibrium lattice constants were in agreement with the available experimental values. The elastic constants (C{sub ij}) were also calculated to understand the mechanical properties and structural stability of the compounds. Furthermore, the density of states and the charge density distributions of the compounds were calculated to understand the nature of the bonding in the material. The calculated results are in accordance with the available data in the literature.
Using density functional theory with the full-potential linearized augmented plane-wave method (FP-LAPW), we have study the structural, electronic, and magnetic properties of Ti{sub 2}FeZ (Z = Al, Ga, and In) alloys with Hg{sub 2}CuTi-type structure. The magnetic stabilities reveal that all our compounds exhibit ferrimagnetic (FiM) behaviors. The electronic structure report the existence of a gap energy equal to 0.56, 0.60, and 0.64 eV for Ti{sub 2}FeAl, Ti{sub 2}FeGa, and Ti{sub 2}FeIn, respectively, in the spin-down state and divulge metallic intersections at the Fermi level for the spin-up state. These results indicate that our compounds have a half-metallic (HM) nature. In addition to this, the total magnetic moments are in agreement with the obtained one by the Slater-Pauling rule (M{sub tot} = Z{sub tot} − 18), which indicates the 100% spin polarization for these compounds.
In this research work, the modified Becke and Johnson potential has been used to realize the actual electronic states and band gap properties of FeAl{sub 2}O{sub 4}. Ferromagnetism is illustrated in terms of John-Teller energy and exchange energies involved in the system due to electron spin. Moreover, the exchange constants also support the ferromagnetism in the studied compound. The reduction of the magnetic moment of Fe from its free space value and the shifting of the magnetic moment to nonmagnetic sites are the consequence of strong magnetization. In the end, the electrical conductivity and Seebeck coefficient incorporated to give a high value of the power factor and thermal efficiency for energy renewable devices.
The full-potential linearized augmented plane wave method within density functional theory was used to investigate the electronic structures, magnetic properties, and half-metallicity in Hf{sub 2}CoZ (Z = B,C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) alloys with AlCu{sub 2}Mn- and CuHg{sub 2}Ti-type structures. The AlCu{sub 2}Mn-type structure is energetically favorable than the CuHg{sub 2}Ti-type structure for all compounds. Hf{sub 2}CoGa, Hf{sub 2}CoAl, Hf{sub 2}CoIn, Hf{sub 2}CoTl, and Hf{sub 2}CoSn compounds in the CuHg{sub 2}Ti-type structure were half-metallic ferromagnets. The d-d and covalent hybridizations between transition metals Hf and Co were effective in the formation of minority band gap. The total magnetic moments of half-metallic Hf{sub 2}CoZ (Z = Al, Ga, In, Sn, and Tl) compounds in the CuHg{sub 2}Ti-type structure obeyed the Slater–Pauling rule (M{sub tot} = Z{sub tot} − 18). Hf{sub 2}CoIn and Hf{sub 2}CoTl compounds were half-metals in relatively wide ranges of lattice constants which indicates that they can be promising and interesting candidates for spintronic devices.
MnS is a semiconductor material that can be used in solar cell coatings as window/buffer material and in many other applications. The present contribution deals with the optical properties of MnS in the zinc-blende structure using ab initio calculations within the generalized gradient approximation. Features such as dielectric function, refractive index, reflectivity, optical absorption, conductivity, and electron loss function spectra have been reported and their pressure dependence has been examined and discussed. The information gathered from the present study can be useful for photovoltaic applications.
In this paper, we performed a density functional theory calculation study on the newly discovered superconductor Re{sub 6}Hf containing anti-symmetric spin-orbit coupling (ASOC) properties. The calculated densities of electronic states demonstrate that the d–d interaction of Re{sub 6}Hf is much stronger than that in Re{sub 6}Zr. A fully relativistic DFT study shows a special performance of densities of states for the spin-up and spin-down electrons. Band structure calculations indicate that the lifting at several high symmetric k points and plenty of splits in band structures yield significant topological transitions in the Fermi surfaces of Re{sub 6}Hf. The energy splitting of bands caused by ASOC are estimated to be 34 and 44 meV, respectively. The de Hass-van Alphen effect simulation is demonstrated and analyzed.
The thermodynamic properties of the tetragonal RNi{sub 2}B{sub 2}C (R=Y, Lu) are investigated by means of the density-functional theory (DFT) and density-functional perturbation theory (DFPT) within the quasiharmonic approximation (QHA). The phonon dispersion curves and phonon total and partial density of states are studied, and it is found that the phonon branches can be divided into three obvious regions: a low-frequency region (LFR), an intermediate-frequency region (IFR), and a high-frequency region (HFR). The temperature dependence of the various quantities including isothermal bulk modulus, thermal expansion coefficient, and heat capacity is obtained, and the variation features of these quantities with temperature are discussed in detail.
We have investigated the half-Heusler compounds RhCrZ (Z = P, As, Sb, Sn). The density functional theory (DFT) framework is employed for the study. We have found that structurally these compounds are stable with lattice constants less than 6.00 Å. Elastically, all the compounds are of ductile nature and anisotropic. We have computed their band gaps in both the spin-down and spin-up channels. It is revealed that they have spin-up channels conducting and spin-down channels having a band gap. Furthermore, investigation of optical properties shows that at lower energies compounds are more active.
The magnetism of undoped and Mn-doped In{sub 2}O{sub 3} has been investigated by employing density functional calculations. For undoped In{sub 2}O{sub 3}, a neutral In vacancy in In{sub 2}O{sub 3} leads to the formation of a net moment of 3 μ{sub B}, which originates from the strong spin polarization of 2p orbitals of O atoms. While, Mn-doped In{sub 2}O{sub 3} system shows robust ferromagnetism which can be attributed to the p-d hybridization between Mn and their neighboring O atoms. In addition, because two O atoms between the two Mn atoms are removed, the ground state of the system have a transformation from the ferromagnetic to the antiferromagnetic state, which further demonstrates that the ferromagnetism is mediated through the p-d interaction.
In this paper, we aimed to study the effect of doping of the compound CdTe with the cobalt impurity (Co), as well as the vacancy defects in Cd sites. On one hand, this leads to the investigation of the magnetic properties and the Faraday rotation effect for the studied alloy, doped with different concentrations of cobalt (0.01, 0.05, 0.1, 0.15, 0.2, 0.25). On the other hand, we have created 0.01 of vacancy defects in Cd sites. Then, we raised the vacancy defect concentration to 0.05, keeping the same concentrations of cobalt. As a result, we have investigated that there is a magnetism appearing with the cobalt doping, while the vacancy defects in Cd sites affect the stability of the magnetic states. In general, it improves the ferromagnetic state that will be well explained in the discussion. Our calculations were performed using the KKR-CPA method within the spin-polarized density functional theory (DFT) with the local density approximation (LDA). The curves of the density of states (DOS) illustrate the results of this study which has been discussed, analyzed, and explained below. In addition, the energy of each case was calculated and given in the tables below for both the DLM (half of the cobalt spins are up while the other half are down) and the ferromagnetic state in order to confirm which one of them is stable.
Based on the density functional theory (DFT), we elucidate the origin of magnetization in non-magnetic cubic halide perovskite CsCdM{sub 3} (M = Cl and Br) induced by substitution of non-magnetic 2p-impurities (B, C, and N) substitution. The calculations were done within the generalized gradient approximation (GGA) and GGA plus-modified Becke and Johnson (mBJ-GGA) as the exchange correlation. The results reveal that half-metallic ferromagnetism can be obtained for C- and N-dopings with the integer magnetic moment of 3.00 and 2.00 µ{sub B} per cell. However, B substitution does not induce magnetism in both CsCdCl{sub 3} and CsCdBr{sub 3} systems. The localized magnetic moments substantially come from impurity atoms. The origin of ferromagnetism can be attributed to the p - p hybridization between 2p-impurities and its surrounding halide atoms. Our results show that doped perovskites could provide a new promising class of materials for future spintronics applications.