Optimization Parameters and Some Electronic Properties of AlSb Diamondoids: A Density Function Theory Study

         استخدمت نظرية دالية الكثافة ضمن المستوي LSDA مع الدالة الاساس3-21G  لفحص الامثلية الهندسية (الزوايا والاواصر) وبعض الخواص الالكترونية التي اشتملت على (طاقة الربط ,فجوة الطاقة والثابت الشبيكي) لجزيئة انتمونايد الالمنيوم في الابعاد النانوية للجزيئات المدروسة باحجامها المختلفة المتمثلة في الجزيئات(الخطية, الحلقية, الثنائيمانتان, والثلاثيمانتان).         اظهرت النتائج ان قيم الزوايا الناتجة تتراوح بين96.21-126.05 degrees)) وكانت مقاربة للزاوية القياسية للجزيئات الماسية والتي تساوي (109.47 degrees) .         وكما اظهرت النتائج ان طاقة الربط للجزيئات المدروسة انها في حالة تناقص مع زيادة عدد الذرات وكذلك نقصان فجوة الطاقة بشكل تدريجي من (5.2-2.1eV) اقترابا من القيمة العملية المدروسة  للمادة في حالتها الصلبة والتي تساوي1.68eV) ) وهذا ما ينطبق على الثابت الشبكي ايضا.        مما سبق نستنتج ان للحجم الجزيئي النانوي تأثير مباشر على الخواص الالكترونية للمادة المدروسة وبالتالي ذلك مما يتيح امكانية استخدامه بالتطبيقات المختلفة وحسب الحاجة .Density function theory with LSDA/3-21G basis set is used to investigate the optimization parameters such as (angles and bonds) and some electronic properties include (cohesive energy, energy gap and lattice constant) of AlSb at nano diamantine and different size of(Linear, Ring, Diamantine and Tetramantine). The results of the present work show that the angles of AlSbH nano molecule in range (96,21-126.05 Å) are near to standard angle of diamond (109.47 Å). Therefore, it is found that the cohesive energy for molecules of studied in decrease state with increase size but the energy gap decreased in gradually shape from (5.2-2.1eV) with increase of the number of atoms, that typical is on the lattice constant. It is finally shown that the size molecules has direct effect on electronic properties to material studied that can used this material in different applications and according to the purpose asked fo

Study the Electronic and Spectroscopic Characteristics of p-n Heterojunction Hybrid (Sn10O16/C24O6) via Density Functional Theory (DFT)

The electronic characteristics, including the density of state and bond length, in addition to the spectroscopic properties such as IR spectrum and Raman scattering, as a function of the frequency of Sn10O16, C24O6, and hybrid junction (Sn10O16/C24O6) were studied. The methodology uses DFT for all electron levels with the hybrid function B3-LYP (Becke level, 3-parameters, Lee–Yang-Parr), with 6-311G (p,d)  basis set, and Stuttgart/Dresden (SDD) basis set, using Gaussian 09 theoretical calculations. The geometrical structures were calculated by Gaussian view 05 as a supplementary program. The band gap was calculated and compared to the measured values. The density of state of the hybrid junction (Sn10O16/C24O6) increased because of the increased number of degeneracy states. Theoretical values of bonds for C=C, C=O, and Sn-O are equal to 1.33, 1.20 and 2.27 Å respectively, these bonds values are in good agreement with experimental values of bond length of 1.34 for the C=C bond, 1.23 for the C=O bond, and 2.3 for the Sn-O bond. . The spectroscopic properties, such as IR spectra have shown a peak which is comparable to longitudinal modes of GO and tin dioxide SnO2 at  (1582 and 690) cm-1, respectively

Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals

Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d) level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å) is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm-1) compared to experimental 0.035 eV (285.2 cm-1). Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å). Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids

Electronic, Structural and Vibrational Properties of GaP Diamondoids and Nanocrystals: A Density Functional Theory Study

The electronic, structural and vibrational properties of gallium phosphide diamondoids and nanocrystals were investigated using density functional theory at PBE/6-31(d) level, which included polarization functions. The energy gap obeyed the quantum confinement size effect with shape fluctuations. The gap converged towards its bulk limit at 2.26 eV. The Ga-P bond lengths of higher diamond‐ oids were found to be distributed around the bulk experi‐ mental value at 2.36 Angstrom. Tetrahedral angles were found around the ideal bulk zincblende value at 109.47, degrees while dihedral angles were distributed around the ideal bulk zincblende values at ±60 and ±180 degree. These findings illustrate that diamondoids are a good represen‐ tative of bulk structure. An analysis of vibrational modes, in terms of reduced masses, force constants and IR intensi‐ ty, was then performed. The size-related change of certain vibrational frequencies of GaP diamondoids was compared with the experimental bulk. Radial breathing mode frequency began from 187 cm-1 for the smallest molecule GaPH6 and decreased with fluctuations, heading to 0 cm-1 as its bulk limit. Longitudinal optical mode began from 187 cm-1 for the smallest molecule and increased with fluctua‐ tions, heading to 376.9 cm-1 (11.3 THz) as its bulk limit. Hydrogen-related vibrations were relatively constant and can therefore be used to identify GaP diamondoids because of their high IR and Raman intensity peaks

Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter) that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001)-(1×1) surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap

Spectroscopic Properties of AlSb Nanocrystals Using Diamondoid Structures: A Density Functional Theory Study

AlSb diamondoids are used as building blocks to investi‐ gate AlSb nanocrystal properties using density functional theory. Energy differences between the HOMO and LUMO of AlSb diamondoids vary according to confinement theory, along with shape fluctuations. AlSb diamondoids’ vibrational force constant reaches 0.82 mDyne/Å, which is less than that of bulk tin. Al-Sb octamantane’s vibrational frequencies and reduced masses reach 334.4 cm-1 and 43.5 amu, respectively. Size variations of UV-Vis show that the maximum optical peak moves from 117 nm to nearly 434.4 nm as the size of the AlSb diamondoids and molecules increases. NMR spectra of AlSb diamondoids are analysed as a function of the diamondoids’ size. 1H-NMR shielding of AlSb diamondoids shows values that are split, in which Al-H shielding is lower than Sb-H shielding. Natural-bond orbital population analysis shows that the present dia‐ mondoids’ bonding differs from ideal diamond sp3 hybridization bonding. The bonding for AlSb electronic orbitals at the centre of AlSb octamantane is Al([core]3s0.913p1.744p0.02) Sb([core]5s1.395p4.056p0.01). The electronic occupation depends on the distance between AlSb atoms and the diamondoid’s surface. AlSb diamond‐ oids’ vibrational longitudinal optical mode is red shifted with respect to the experimental bulk value, which is the case for C and Si