Papers by Keyword: First Principles

Abstract: In order to analyze the influence of Al-Ag doping on the electrical properties of eigenstate and oxygen vacancy ZnO resistor valves, first principles were used to analyze the crystal structure of Al-Ag single doping and co-doping eigenstate and oxygen vacancy ZnO. Energy, band structure, density of states and electrical conductivity have been calculated. The results show that after doping with acceptor elements, the lattice parameters of the eigenstate unit cell and the oxygen vacancy unit cell are increased, and their potential can be increased. Gradient; when Ag is doped, its formation energy is the lowest, indicating that Ag doping is easier and higher stability; when oxygen vacancies, the nonlinear characteristic of ZnO resistor valve is better than that of eigenstate, but whether it is single doping or Co-doping does not improve its nonlinear characteristics better; doping will slightly increase its conductivity, and the conductivity of Ag doping is the best.

Abstract: Understanding and controlling the phonon, the dominant heat carrier of semiconductor materials, is essential to developing a wide variety of applications. This article studies the theoretical and computational approach of the calculation of lattice thermal conductivity of semiconducting materials. Despite having different methods to calculate the lattice thermal conductivity, first-principle estimates predict more accurately in most applications. This motivates to present the descriptive explanation on first-principle calculation with the combination of lattice dynamics and Boltzmann transport equation. Finally, we summarized an overview of the recent achievements and opportunities.

Abstract: Layered lithium iron hydroxysulfate, LiFeSO₄OH was recently proposed as a cathode material for lithium ion batteries (LIBs) made up of low cost and sustainable components. Here, we report ab-initio investigation into the structural properties of its sodium analogue, NaFeSO₄OH obtained from in-situ substitution of lithium (Li) with sodium (Na). A robust host structure for NaFeSO₄OH was discovered owing to strong Fe-O and S-O bonds, a good indicator for thermal stability and long cycle life. The Na ions are strongly held by the oxygen atoms, but the charge density map proves that the bond between the two is still ionic.

Abstract: The search for clean energy conversion technologies promotes the study of thermoelectric materials. In this paper, the electronic structure and thermoelectric properties of CaMnO₃ doped with 17% V using first principles calculations and semi-classic Boltzmann theory on Ca site as well as Mn sites. The G-type AFM magnetic ordering is most stable among four types of magnetic ordering for CaMnO₃ and V doped CaMnO₃ a Mn site while FM ordering was found for V doped CaMnO₃ at Ca site. The calculated partial density of states plot shows half metallic and metallic behavior for V doped at A site and B site respectively. Thermoelectric property calculations show that the magnitude of Seebeck coefficient decreased with V doping at both sites with V doping at Mn sites has the lowest magnitude of Seebeck coefficient. All samples show the negative Seebeck coefficient indicating n type behavior. The magnitude of conductivity increases with V doping with the highest magnitude belong to V doped at Mn site. The magnitude of thermal conductivity also increased with V doping at Mn site, but shows a reduction for V doping at Ca site. The figure of merit (ZT) for V doping at Ca site shows a significant improvement over intrinsic CaMnO₃ at 0.14 at 1000 K. However, V doping at Mn site sample shows a reduction of ZT at 0.0028 for CaMnO₃ at 1000 K which is much lower than CaMnO₃ at 0.08.

Abstract: The electronic structure and thermoelectric properties of CaMnO₃ doped with 8% and 17% f block element Sm using first principles calculations and semi-classic Boltzmann theory were presented in this paper. The G-type AFM phase is most stable among five phases for CaMnO₃, however, with 8% and 17% Sm doping, these compounds became nonmagnetic phases. CaMnO₃ calculated electronic band structure shows an indirect band gap of 0.523 eV, which is underestimated by the density functional theory (DFT) calculations but the band gap explains the semiconducting behavior. However, with 8% and 17% Sm doping, the electronic bandstructure of these compounds exhibit metallic behavior, with Sm and Mn 3d electrons contributing to conduction band, increasing the magnitude of conductivity for doped compounds. All temperature dependence Seebeck coefficient plots show n-typed conduction for all compound with reduced magnitude of Seebeck coefficient for doped compounds. The temperature dependence thermal conductivity plot shows overall thermal conductivity is reduced in Sm doped compound. CaMnO₃ with 17% Sm doping exhibit much higher ZT of 0.32 at 800 K showing enhanced thermoelectric properties at high temperature and suitability or high temperature energy conversion devices.

Abstract: Based on the first principles and quantum mechanics, a new approach is put forward to calculate the cohesive energy of face-centered cubic solid neon, in which both the two-body and the total many-body interaction potentials are reasonably emphasized by a new combination formula. It shows that the new scheme is a simple and accurate tool to understand the high-pressure behaviors of solid neon, and it will be applied to calculate the compression curves of dense Helium, Argon, Krypton and Xenon at very high pressures. It is expected that this method can be applicable to all rare gas, including the gas, solid, and liquid phase regions, even of molecular systems, ionic systems.

Abstract: Investigation on structure and electronic structure under external electric field is a very interesting subject. To investigate the evolution of structure and properties from the perspective of electronic structure, the configuration of NaCl crystal has been calculated with the first principles in different external electric field. The system of energy, bond length, geometrical, radial distribution function, difference charge density, and density of states has been carefully examined. The analysis of the calculated results suggested that, with the increasing of external electric field, the system energy presents the roughly increases to a maximum value then begin to decrease, the long range structure become more disordered, the geometrical structure is significantly influenced, the iconicity of NaCl enhances.

Abstract: In this paper, the effect of substitution of Co by d-valent elements such as Ag and Pt on electronic structure and magnetic properties of full Heusler type Co₂FeSi alloys was investigated. Structural study reveals the presence of a small gap in the minority band structure around the vicinity of the Fermi level on Co₂FeSi resulting to half-metallic behaviour. However, CoFeSiAg and CoFeSiPt cannot preserved the half-metalicity due to disappearing of the gap in the minority band structure due to the creation of new states around the Fermi level in the minority density of states. The variation in the magnetic moment of Co₂FeSi with change of the atoms was attributed to the change in the local magnetic moment of atoms.

Abstract: In this study, first principles calculations based on density functional theory were used to evaluate optimized sructures and the total energy of the La doped PbTiO₃ tetragonal (P4mm phase group). The calculations were conducted using local density approximation (LDA) functional as implemented in Cambridge Serial Total Energy Package (CASTEP) computer code. The different composition of Lanthanum (x) were doped on PbTiO₃ resulting Pb_1-xLa_xTiO₃ and its effect on the structural of Pb_1-xLa_xTiO₃ were investigated. The different composition of La changed the lattice parameter and the volume of Pb_1-xLa_xTiO₃. The total energy also were calculated and x= 0.2 is suitable composition of dapant to doped with PbTiO₃ which is more stable compared with the other composition. The results are compared with experimental and other theoretical data.

Abstract: Double metal amidoborans are considered to the most promising candidates for metal amidoborans. In this paper, the crystal structures, electronic properties, chemical bonds, hydrogen removal energies, and HOMO-LUMO of NaAB, NaLiAB, and NaMgAB have been studied. The GGA corrected density functional theory have been employed in the first principles calculations. Due to the alkali and alkali earth metals coexisting, the crystal structures of these compounds change significantly and the B–H, N–H and B-N bond lengths shorten. Moreover, the band structures and density of states of NaAB, NaLiAB, and NaMgAB were calculated. The charge density distributions and bond populations are used to understand the nature of bonding. The hydrogen removal energy states removing H(B) and H(N) from NaLiAB more easily than NaAB and NaMgAB. In addition, the frontier molecular orbital reveals that the intermolecular and intramolecular dehydrogenation of NaLiAB and NaMgAB may concur. The calculated HOMO-LUMO energy gaps suggest that the chemical reactivity is: NaLiAB> NaAB> NaMgAB.