Theoretical Study of the Electronic Properties of The Curcumin Molecule: Using Density Functional Theory

يهدف البحث الى دراسة الخواص الالكترونية لجزيئة الكركمين والتي توجد في صيغتين أيزوميريتين صيغة الكيتون والأينول وتأثير أستخدام دوال أساس مختلفة من خلال الاعتماد على نظرية دالية الكثافة عند المستوي B3LYP. أنتقال ذرة الهيدروجين من مجموعة الميثيلين المركزية(CH2)  لترتبط بذرة الأوكسجين حتى تشكل أصرة هيدروجينية(O H)  يسبب تغيرات هندسية في شكل الأيزوميرين, حيث شكل الأينول هي تركيب خطي   تقريبا ولكن شكل الكيتون ليس خطي تماما. الدالة 6-311G+(d,p) أعطت نتائج مقنعة للحسابات. كذلك حسابات كل من الطاقة الكلية و طاقة أعلى مدار جزيئي ممتلئ وفجوة الطاقة أكدت أن الكيتون هو الأكثر أستقرارا من الأينول. وأيضا الكيتون لديه قابلية عالية لقبول الألكترونات كما ثبت من خلال قيم كل من طاقة أوطأ مدار جزيئي غير ممتلئ وجهد التأين والألفة الألكترونية و الكهروسالبية.This search aims to study electronic properties of the curcumin moleculewhich exist in two isomers, ketone and enol forms, and the effect of usingdifferent basis setsby relying on density functions theory (DFT) at B3LYP level. The hydrogen atom transfer from the central methylene (CH2) group to an oxygen atom to form strong intra-molecular hydrogen (O H) bond causes geometrical changes in two isomers; where the enol form is structure approximately planar but not completely planar for the ketone form.The results showed that the 6-311G+(d,p) basis set gave sat- isfactory results for calculations. As well as the findings of each of the total energy, the energy of the high occupied molecular orbital and energy gap confirm that the isomer ketone is more stable than isomer enol. Also the ketone has a high electron-accepting, as was proven by the values of the energy of lower unoccupied molecular orbital,ionization potential, electron affinity and electronegativity

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

Tuning thermoelectric properties of graphene/boron nitride heterostructures

Using density functional theory combined with a Green's function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to -284 μv K(-1) and doping by the electron acceptor tetracyanoethylene increases S to 210 μv K(-1). After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained

Degradation of Indigo Dye Using Quantum Mechanical Calculations

The semiempirical (PM3) and DFT quantum mechanical methods were used to investigate the theoretical degradation of Indigo dye. The chemical reactivity of the Indigo dye was evaluated by comparing the potential energy stability of the mean bonds. Seven transition states were suggested and studied to estimate the actually starting step of the degradation reaction. The bond length and bond angle calculations indicate that the best active site in the Indigo dye molecule is at C10=C11.  The most possible transition states are examined for all suggested paths of Indigo dye degradation predicated on zero-point energy and imaginary frequency. The first starting step of the reaction mechanism is proposed. The change in enthalpy, Gibbs free energy and change in entropy of the overall reaction are equal to -548268.223 kcal/mol, 30831.951 kcal/mol and 48.552 cal/mol.deg, respectively. The activation energy is 46176.405 kcal/mol. The reaction rate is equal to

Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations

Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces 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