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Ab initio wavefunction based methods are applied to the study of electron correlation effects on the band structure of oxide systems. We choose MgO as a prototype closed-shell ionic oxide. Our analysis is based on a local Hamiltonian…
Density functional theory (DFT) calculations of defect levels in semiconductors based on approximate functionals are subject to considerable uncertainties, in particular due to inaccurate band gap energies. Testing previous correction…
Hybrid functionals and empirical correction schemes are compared to conventional semi-local density functional theory (DFT) calculations in order to assess the predictive power of these methods concerning the formation energy and the charge…
Density-functional studies of the electron states in the dilute magnetic semiconductor GaN:Mn reveal major differences for the case of the Mn impurity at the substitutional site Mn_Ga versus the interstitial site Mn_I. The splitting of the…
Ion implantation is a non-equilibrium doping technique which introduces impurity atoms into a solid regardless of thermodynamic considerations. The formation of metastable alloys above the solubility limit, minimized contribution of lateral…
Mn is used as a dopant to improve the electromechanical properties of perovskite oxides. We elucidate the role of Mn defects and associated vacancies on the electronic, atomic and ferroelectric properties of BaTiO$_3$. Using density…
Chemical nature of point defects, their segregation, cluster or complex formation in ZnO is an important area of investigation. In this report, 1.2 MeV Ar ion beam is used to incorporate defects in granular ZnO. Evolution of defective state…
The electronic structure and optical absorption spectrum of V^{0} and V^{-} center in MgO are investigated using first-principles calculations based on density functional theory. It is demonstrated that the configuration with distortion is…
Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. Here we consider such charge storage in a series of oxygen deficient phases of TiO$_2$, known as Magn\'eli phases. These…
Cubic hafnia (HfO$_2$) is of great interest for a number of applications in electronics because of its high dielectric constant. However, common defects in such applications degrade the properties of hafina. We have investigated the…
A band structure description of the observed large band gaps and moments in both the antiferromagnetic (AFM) and paramagnetic (PM) phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO is provided by ordinary,…
The magneto-optic Voigt effect is observed in a synthetic diamond membrane with a substitutional nitrogen defect concentration in the order of 200 ppm and a nitrogen-vacancy defect sub-ensemble generated through neutron irradiation and…
We investigate the behavior of oxygen vacancies in three different metal-oxide semiconductors (rutile and anatase TiO2, monoclinic WO3, and tetragonal ZrO2) using a recently proposed hybrid density-functional method in which the fraction of…
Formation and excitation energies as well charge transition levels, are determined forthe substitutional nitrogen (Ns),the vacancy (V) and related point defects (NV, NVH, N2, N2V and V2) by screened non-local hybrid density functional…
This work involves the local structural investigation of the samples using Extended X-ray Absorption Spectra (EXAFS) analysis to investigate structural changes due to the Ca and Mn-modified BaTiO3. TEM investigation of the crystal structure…
We present an improved method to calculate defect formation energies that overcomes the band-gap problem of Kohn-Sham density-functional theory (DFT) and reduces the self-interaction error of the local-density approximation (LDA) to DFT. We…
Oxygen is the most common unintentional impurity found in GaN. We study the interaction between substitutional oxygen (ON) and the gallium vacancy (VGa) to form a point defect complex in GaN. The formation energy of the gallium vacancy is…
In this work, the electronic and optical properties of a Nitrogen (N) or a Boron (B) doped BeO monolayer are investigated in the framework of density functional theory. It is known that the band gap of a BeO monolayer is large leading to…
The different crystal structures of ferromagnetic Ni$_2$MnGa have been calculated using density functional theory (DFT) with special emphasis on the modulated structures 10M and 14M. These are important for understanding the stability of…
Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce…