Mohammad Ebrahim Ghazi

Bio: Mohammad Ebrahim Ghazi is an academic researcher from University of Shahrood. The author has contributed to research in topics: Density functional theory & Band gap. The author has an hindex of 15, co-authored 66 publications receiving 583 citations. Previous affiliations of Mohammad Ebrahim Ghazi include Durham University.

DFT Study of Mechanical Properties and Stability of Cubic Methylammonium Lead Halide Perovskites (CH3NH3PbX3, X = I, Br, Cl)

Abstract: In this study, using the density functional theory, the mechanical properties of methylammonium lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) were investigated. Young’s modulus, bulk modulus, and shear modulus, Poisson’s ratio, and many other parameters were calculated using the PBEsol and vdW approximations. Also, in this work, utilizing a new accuracy in calculating the elastic constants, the intense conflict between the previous theoretical results and the experimental data were fixed. Moreover, for the first time, through combination of the PBEsol and vdW methods, the effect of the interaction between methylammonium and PbX3 scaffold on the mechanical properties of lead halide perovskites was well cleared. In continuation, using the PBEsol+vdW method, a phase transition appeared for the MAPbBr3 and MAPbCl3 structures, which proved more stability of MAPbBr3 and MAPbCl3 in comparison with MAPbI3. In what follows, by studying these materials under an applied strain beyond the harmonic region, the t...

Tunable magnetic and magnetocaloric properties of La0.6Sr0.4MnO3 nanoparticles

Abstract: Nanoparticles of La0.6Sr0.4MnO3 with different particle sizes are synthesized by the nitrate-complex auto-ignition method. The structural and magnetic properties of the samples are investigated by X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, transmission electron microscopy (TEM), and DC magnetization measurements. The XRD study coupled with the Rietveld refinement shows that all samples crystallize in a rhombohedral structure with the space group of R-3 C. The FT-IR spectroscopy and TEM images indicate formation of the perovskite structure with the average sizes of 20, 40, and 100 nm for the samples sintered at 700, 800, and 1100 °C, respectively. The DC magnetization measurements confirm tuning of the magnetic properties due to the particle size effects, e.g., reduction in the ferromagnetic moment and increase in the surface spin disorder by decreasing the particle size. The magnetocaloric effect (MCE) study based on isothermal magnetization vs. filed measurements in all samples reveals a relatively large MCE around the Curie temperature of the samples. The peak around the Curie temperature gradually broadens with reduction of the particle size. The data obtained show that although variations in the magnetic entropy and adiabatic temperature decrease by lowering the particle size, variation in the relative cooling power values are the same for all samples. These results make this material a proper candidate in the magnetic refrigerator application above room temperature at moderate fields.

Studying temperature effects on electronic and optical properties of cubic CH 3 NH 3 SnI 3 perovskite

Abstract: CH3NH3SnI3 is a promising lead-free perovskite structure for the absorber layer in solar cells. In this work, for the first time, we simulated the effect of temperature change on the electronic and optical properties of CH3NH3SnI3 through a combination of the molecular dynamics and density functional theory methods. We report the results of our studies on the electronic and optical properties of the normal (300 K) and expanded (325 K)/contracted (275 K) CH3NH3SnI3 structures, and compare the obtained results with each other. Our electronic calculations showed that the direct band gap is opened up to 1.02 eV, 1.25 eV, and 0.88 eV for the normal and thermally expanded/contracted structures, respectively. The calculated density of states for all the structures shows that the Sn and I ions play an important role in the electronic properties of the studied samples, and methyl ammonium (CH3NH3) is a structural framework for this perovskite. The absorption, transparency, and maximum reflectivity to the considered energies indicate the potential of CH3NH3SnI3 for optoelectronic applications. The obtained results also show that the CH3NH3SnI3 perovskite, as an absorber layer in solar cells, exhibits a better optical performance at 325 K than at 275 K and 300 K.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Colossal dielectric constants in transition-metal oxides

Abstract: Many transition-metal oxides show very large (“colossal”) magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today’s most investigated material with colossal dielectric constant Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2−xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Abstract: We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.