Papers by Keyword: Total Energy

Abstract: Terrestrial vertebrates can walk more elegant than any other man-made legged mechanical models, which yield unstable locomotion with low speed. They continuously have modified their body structure and living patterns for the survival. They still continue their development. Legs are basically a serial linkage of rigid bodies connected by joints and exactly correspond to the manipulator in robot. Structure of living creatures are copied and modeled with 12 links, 12 joints and body, from the mechanical engineering viewpoint. Iterative Newton-Euler method is applied to compute torques acting all joints, which are required to calculate the total consumed energy to complete one locomotion cycle. Mechanical energy efficiency of different variables or systems are evaluated and compared by specific resistance. Parameters, specifying structure and locomotion, are applied to the simulation and the optimal values which minimize energy expenditure in locomotion are derived.

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: Paper presents the modelling of the contact problem in the technological processes. Technological processes were considered as a geometrical and physical boundary and initial value problem, with unknown boundary conditions in the contact zone. An incremental model of the contact problem between movable rigid or elastic body (tool) and elastic/visco-plastic body (object) in updated Lagrange formulation, for spatial states (3D) was considered. The incremental functional of the total energy and variational, non-linear equation of motion and deformation of object on the typical step time were derived. This equation has been discretized by finite element method, and the system of discrete equations of motion of objects was received. For solution of these equations the explicit or implicit methods was used. The applications were developed in the ANSYS/LS-Dyna system, which makes possible a complex time analysis of the states of displacements, strains and stresses, in the workpieces in technological processes. Application of this method was showed for examples the modelling and the analysis of tensile test [1 and technological processes of metal forming [1-.

Abstract: In the present investigation, we report theoretical study of total energy, energy band gap in X-direction, bulk modulus, elastic constants and pressure derivative of elastic constants of Si_1-xSn_xsolid solution using higher-order perturbation theory along with application of our proposed potential, where x is concentration of Sn. The parameter of our potential is determined using zero-pressure equilibrium condition. In the present calculations, The local-field correction function can be employed to consider exchange and correlation effects. The present study showed that the physical quantities under investigation varied with the concentration of the constituent element.

Abstract: The crystal structure models of three kinds of different Al(OH)3 crystals, which are gibbsite, bayerite and nordstradite, are built respectively according to the corresponding experimental crystal lattice. Geometry optimizations are implemented by CASTEP program module using general gradient approximation (GGA) and local density approximation (LDA) methods respectively based on density functional theory (DFT). Total energy, electronic structure, atomic and bond populations are also calculated. The calculation results of total energy indicate that gibbsite is steadier than the other two from the point of view of energy, and the effect of basis set of GGA-PW91 is highest. At the same time, energy bond structure and density of states calculated at GGA-PW91 and LDA-CA-PZ levels show that the different of energy gap ΔE (ELUMO-EHOMO) at the first group of BZ is not obvious, and that the highest value of ΔE of gibbsite is more lower than the other two Al(OH)3 crystals. It may be likely to say that gibbsite may be more active than the other two crystals. According to the analysis of populations, it can be found that bond populations value of H-O and Al-O bonds of gibbsite is smallest in three different Al(OH)3 crystals, it is to say that the combination force of H-O and Al-O bonds of gibbsite is smallest and gibbsite may be more easier to be calcined theoretically.

Abstract: We have performed first principles total energy calculations to investigate the structural properties of copper iodide (CuI) in its sodium chloride, cesium chloride, zincblende and wurtzite structures. Calculations are done using the density functional theory. We employ the full potential linearized augmented plane wave method as implemented in the wien2k code. The exchange and correlation potential energies are treated in the generalized gradient approximation (GGA), and the local density approximation (LDA). Optical absorption experiments and x-ray diffraction measurements have shown that zincblende is the ground state of CuI. Our calculations find that in the GGA formalism wurtzite and zincblende have similar total energies, while in the LDA formalism the lowest minimum corresponds to zincblende. Results show that the energy difference between the wurtzite and the zincblende structures, as calculated within the GGA formalism is 2 meV, and within the LDA formalism, is 31 meV. These results may suggest a coexistence of both wurtzite and zincblende structures in the ground state of CuI. Structural parameters are correctly reproduced by the GGA calculations. We obtain that under the application of external pressure the atomic configuration may transform into the NaCl structure. At higher pressures it is possible to have a phase transition to the CsCl geometry.

Abstract: The electronic and structural properties of different members of the Ni-Mn-Ga family calculated by ab initio density functional theory are discussed. From total energy calculations, we show that the martensitic phase is the stable low temperature phase. Moreover, occurrence of ferromagnetic and paramagnetic martensitic phases for Ni2MnGa and Ni2.25Mn0.75Ga, respectively, are explained. Modifications in the density of states near the Fermi level EF are observed across the martensitic transition for Ni2MnGa, as well as in Mn2NiGa. While Ni2MnGa is ferromagnetic, we find Mn2NiGa to be ferrimagnetic. The calculated lattice constants and the magnetic moments are in good agreement with experiment.