محاسبه كوانتومي خواص ساختاري، الكتروني، مغناطيسي و ديناميكي نانو خوشه هاي...

چكيده انگليسي :

Quantum Mechanical Calculation of Structural Electronic Magnetic and Dynamical Properties of Con and Con 1Au n 6 Nanoclusters Mahdieh Aghajani Garmejani maghajani ph@gmail com Date of Submission 2011 2 20 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Persian Supervisor Hadi Akbarzadeh akbarzad@cc iut ac ir Abstract Magnetic nanoparticles such as Cobalt nanoclusters exhibit superparamagnetic and ferromagnetic behaviors controlled by the particle size and interaction Superparamagnetism is a distinctive behavior of single domain nanoparticles originated from the fast flipping process of the total magnetic moment due to thermal energy Superparamagnetic nanoparticles have widespread biomedical applications such as drug delivery hyperthermia and magnetic resonance imaging MRI The high surface area to volume ratio of nanoparticles results in oxidation in the air Ferromagnetic nanoparticles with their antiferromagnetic oxidized shell e g Co CoO have shown an exchange bias effect Although this effect is useful for magnetic recording and Spintronics application it prevents superparamagnetism Hence for biomedical application Co nanoparticles are coated with Gold Au shell to prevent surface oxidation Therefore accurate theoretical understanding of Au Co nanoparticle interaction would be helpful for improving their biomedical application In this thesis absorption of one Au atom on Co nanoclusters is investigated in the framework of density functional theory DFT calculations by using the all electron full potential code FHI aims Fritz Haber institute ab initio molecular simulations FHI aims employs atom centered numerical orbitals basis set that is both computationally efficient and accurate This package allows to describe the electronic single quasi particle excitations in non periodic cluster geometries using GW many body perturbation theory First we report the calculated structural electronic and magnetic properties of bulk Co Accuracy of FHI aims results is confirmed by recalculating and comparing some parts of the results with WIEN2k package Comparing the obtained Co dimer results within five different exchange correlation functionals such as PW LDA BLYP RPBE PBE and PBEsol we observed better performance of BLYP functional for Co nanoclusters hence rest of calculations were carried out with this functional Stable geometries binding and dissociation energies ionization potentials electron affinities HOMO LUMO gaps magnetic properties vibrational frequencies and infrared absorption spectrums of Co n and Con 1Au n 6 nanoclusters are calculated in the scalar relativistic collinear magnetic level The stable structures of Co nanoclusters mainly are obtained to be three dimensional It is explained that the Jahn Teller effect plays an important role in the stable structure of cobalt nanoclusters Adding one Au atom to dimer trimer and tetramer Co nanoclusters resulted in one or two dimensional structures because of high sd hybridization in bonds between Au and Co atoms Magnetic moments of Co atoms are aligned ferromagnetically and are enhanced with respect to the bulk value It is observed that the magnetic moments are more sensitive to the average coordination number relative to the average bond length Absorption of one Au atom decreases magnetization because of deduction of symmetry and average coordination number of nanoclusters Considering electronic chemical and dynamical stability magic number of Co nanoclusters is concluded to be six and somewhat four while the most stable Con 1Au nanoclusters was found to be Co3Au We showed that the GW correction significantly improves the ionization potentials electron affinities and HOMO LUMO gaps toward experimental values Keywords Density functional theory DFT All electron full potential package FHI aims atom centered numerical orbitals NAO Cobalt magnetic nanoclusters Con Absorption of Gold Au atom GW correction

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محاسبه كوانتومي خواص ساختاري، الكتروني، مغناطيسي و ديناميكي نانو خوشه هاي...