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- 저자 : F. Ahmadian (검색결과 4 건)
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First-principles Study on the Structural, Electronic, and Optical Properties of Ca1−xSrxSe Alloys
F. Ahmadian,A. Salary 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.2
The structural, electronic, and optical properties of binary CaSe and SrSe compounds and Ca1−xSrxSe alloys were studied by using the full potential linearized augmented plane wave (FPLAPW) method within density functional theory (DFT). The band structure calculations showed that the CaSe and the SrSe binary compounds in the rocksalt (RS), zinc-blende (ZB) and wurtzite (WZ) phases were semiconductors while they had a metallic characteristic in the CsCl phase. The lattice constant and bulk modulus values for the Ca1−xSrxSe alloys in the RS and the ZB phases at different concentrations were calculated and compared with those obtained by using Vegard’s law. The energy band gap values in the RS and the ZB phases were estimated for different x values by using both define acronyms the Perdew, Burke, and Ernzerhof (PBE-GGA) and the Engel and Vosko (EV-GGA) schemes, and the results were compared with those obtained by using the empirical electronegativity expression. The band gap bowing parameters were calculated by using quadratic functions and the procedure of Bernard and Zunger to fit the non-linear variation of the band gaps. The static dielectric constant "1(0) was calculated at different concentrations. The energy loss function L(!) for the Ca1−xSrxSe alloys in the RS and the ZB phases has a main peak corresponding to the plasmon frequency. The values of the static refractive index (n(0)) for the Ca1−xSrxSe alloys were calculated and compared with the values predicted by using the Moss, Ravindra, and Vandamme models. Finally, the extinction indic incident photon energies. es (k(!)) and the reflectivities (R(!)) for the Ca1−xSrxSe alloys were calculated within a wide range of incident photon energies.
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Half-metallicity in a New Heusler Alloy Ti2FeSn: A Density Functional Study
F. Ahmadian 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.2
First-principles calculations based on density functional theory for a new Heusler compoundTi2FeSn have been performed using the self-consistent full-potential linearized augmented planewave method. The results showed that the Ti2FeSn Heusler alloy was a half-metallic ferrimagnet. The obtained total magnetic moment of Ti2FeSn was 2 μB per formula unit for the equilibriumlattice parameter, which is in agreement with the Slater-Pauling rule (Mtot = Ztot − 18). Thecalculated minority spin and spin-flip gaps were 0.79 eV and 0.38 eV, respectively. In addition,the band structure and the density of states were studied, and the reason for the appearance of aminority band gap is discussed. The Ti2FeSn alloy kept a 100% spin polarization at the Fermi leveland had a half-metallic characteristic for lattice constants from 5.5 to 6.7 ˚A showing that it is aninteresting material in the field of spintronics
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A. Eftekhari,F. Ahmadian 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.9
The electronic structures, magnetic properties and half-metallicity in Zr2RuZ (Z = Ga, In, Tl, Ge, Sn, and Pb) alloys with AlCu2Mn- and CuHg2Ti-type structures were investigated using firstprinciples density functional theory (DFT) calculations. The calculations showed that Zr2RuIn, Zr2RuTl, Zr2RuSn, and Zr2RuPb compounds with CuHg2Ti-type structures were half-metallic ferromagnets with half-metallic band gaps of 0.18, 0.24, 0.22, and 0.27 eV, respectively. The halfmetallicity originated from d-d and covalent hybridizations between the transition metals Zr and Ru. The total magnetic moments of the Zr2RuZ (Z = In, Tl, Sn, and Pb) compounds with CuHg2Titype structures were integer values of 1B and 2B, which is in agreement with Slater-Pauling rule (Mtot = Ztot 18). Among these compounds, Zr2RuIn and Zr2RuTl were half-metals over relatively wide regions of the lattice constants, indicating that these two new Heusler alloys are ideal candidates for use in spintronic devices.
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Causes of Common and Frequent Claims in Oil, Gas and Petrochemical Projects of Iran
S. H. Hasheminasab,M. M. Mortaheb,A. Ahmadian F. F. 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.5
Over recent years, frequent involvements in claims have been inevitable due to unpredictable economic changes and increasingcomplexities in construction industry. Therefore, even appropriately made contracts are not exempted from claims. On the otherhand, construction contract claims are time-consuming, expense-involving and most likely leading to unsatisfactory results. However, there may be some positive outcomes, such as time extension or compensation of damages. To launch investigations, a listof important and frequent claims in oil and gas industry projects of Iran was extracted after a succinct documents review. Further, themost important claim causes were identified through conducting a questionnaire survey among contractors, consultants, owners andlawyers involved in such projects. Reliability of responses has been examined, accordingly. The study reveals that the external riskslike political, social, cultural and economical issues are the most important causes for claims in this industry. Moreover, inadequatefinancial resources on the part of owner and contractor, failure in performing contractor’s obligations and vague contract conditionsresulted in formation of different interpretations; are some of the most important root causes of claims in this context.
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