5644

351 دكتري

دكتري

ماده چگال محاسباتي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1389

[ده]، [109]ص:مصور، جدول، نمودار.

ص.ع.به فارسي و انگليسي

هادي اكبرزاده

جواد هاشمي فر، اكبر جعفري

18/11/89

فيزيك

ID351 دكتري

به فارسي و انگليسي: قابل رويت در نسخه ديجيتال

First principle study of 1 Charged Oxygen vacancies in rutile TiO2 2 Structural stability of narrow hexagonal MnAs nanowires Ali Kazempour kazempoor@ph iut ac ir January 4 2011 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Hadi Akbarzadeh supervisor akbarzad@cc iut ac ir Seyed Javad Hashemifar advisor hashemifar@cc iut ac ir Seyed Akbar Jafari Advisor jafari@physics sharif ir F Shahbazi Abstract In this thesis in the first part using first principle method we investigated charged Oxygen vacancies in rutile TiO2 by exploiting gap correction approach such as GGA U GW many body correction and hybrid functional Although GGA U improve the character of localized d orbitals and also enlarge the band gap but it would be unable to give the neutral and singly ionized vacancy induced levels inside the gap and stabilize them We apply GW on top of GGA U which is better starting point and closer features to the quasiparticle picture than GGA The obtained results shows that application of GW correction severely depends on and follows the behavior of the starting point and therefore cannot stabilize the neutral and singly ionized vacancy in the gap Moreover In the whole variation of Fermi energy across the gap singly ionized vacancy is never stable Employing hybrid functional PBE0 and HSE in addition to gap correction would transfer the neutral and singly ionized vacancy states into the gap in qualitative agreement with experiment Also the results shows doubly ionized vacancy have lower formation energy in Ferrni energy variation Hence oxygen vacancy is shallow donor with the doubly ionized vacancy is the most stable charge In the second part we performed ab inito methods to the investigation of Mn and As centers magnetic nanowires Using two phenomenological models based on dangling bond energies and position dependent atomic energies show periodic behavior of stability which originate from edge energy and compositions Additionally using ab initio thermodynamics in real temperature and pressure all phase diagram show periodic stability in which the magnetic edges is undesirable Key Words Ab initio nanowire oxygen vacancy TiO2 MnAs formation energy GWA Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Department of Physics Sharif University of Technology Tehran 11365 9161 Iran Introduction Transition metal oxides are one of the most important category of material in which ab initio methods fail to describe their properties properly The reason lies in the fact that they posses complex structure and cover wide range of optical magnetic electrical and semiconducting

هادي اكبرزاده

جواد هاشمي فر، اكبر جعفري