Comprehensive Ab Initio Study of Electronic, Optical, and Cohesive Properties of Silicon Quantum Dots of Various Morphologies and Sizes up to Infinity

We present a comprehensive and integrated model-independent ab initio study of the structural, cohesive, electronic, and optical properties of silicon quantum dots of various morphologies and sizes in the framework of all-electron "static" and time-dependent density functional theory (DFT, TDFT), using the well-tested B3LYP and other properly chosen functional(s). Our raw ab initio results for all these properties for hydrogen-passivated nanocrystals of various growth models and sizes from 1 to 32 Å are subsequently fitted, using power-law dependence with judicially selected exponents, based on dimensional and other plausibility arguments. As a result, we can not only reproduce with excellent accuracy known experimental and well-tested theoretical results in the regions of overlap but also extrapolate successfully all the way to infinity, reproducing the band gap of crystalline silicon with almost chemical accuracy as well as the cohesive energy of the infinite crystal with very good accuracy. Thus, our results could be safely used, among others, as interpolation and extrapolation formulas not only for cohesive energy and band gap but also for interrelated properties, such as dielectric constant and index of refraction of silicon nanocrystals of various sizes all the way up to infinity. © 2016 American Chemical Society

SURFACE CORE LEVEL SHIFT OF BERYLLIUM. X-RAY RAMAN SPECTRUM OF A Be THIN FILM

The bonding characteristics and the inner core 1s binding energy of an one-dimensional Be film is studied in comparison to the bulk Be metal. The difference in the 1s binding energy is calculated very accurately together with the variation of the bonding characteristics responsible for the appearance of anomalous peaks in the x-ray Raman spectrum of Be metal

ANOMALOUS X-RAY RAMAN SPECTRUM OF POLYCRYSTALLINE BORON

The anomalous peaks in the x-ray Raman spectrum of polycrystalline boron have been examined experimentally and theoretical1y. These peaks are associated with d-like atomic states high in the conduction bands, The "anomalous" nature of these peaks is also manifested in their angular dependence

CALCULATION OF INNER CORE ELECTRON BINDING ENERGIES IN METALS

Employing state specific total energy differences between the core hole and the ground Hartree-Fock cluster states. We obtain the ƊSCF binding energy of inner core electrons in metals. This ƊSCF value, enhanced by atomic correlation and relativity effects can provide inner core electron binding energies in very good agreement with experiment. Results have been obtained thus far for Li , Be, Mg and Na metals

Aromaticity of planar Si-6 rings in silicon-lithium clusters

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Theoretical calculation of Tc for lead

Using our ab initio band structure results, we calculate the transition temperature of Pb according to the Gaspari-Gyorffy theory. The calculated value is half the experimental one. The discrepancy is attributed to the rigid muffin tin approximation. A simple method with no adjustable parameters is developed to account for this approximation. The new transition temperature is in excellent agreement with experiment.Nous calculons la température de transition supraconductrice du Pb avec la théorie de Gaspari et Gyorffy, en utilisant nos calculs ab initio de structure de bande. La valeur calculée ainsi est la moitié de la valeur expérimentale. Cet écart est attribué à l'approximation du potentiel muffin tin rigide. Pour tenir compte de cette approximation nous présentons une méthode simple, sans paramètre ajustable. La nouvelle valeur calculée de la température de transition est en accord excellent avec la valeur expérimentale

Ab initio bandstructure of lead

The self-consistent semi-relativistic APW method has been employed to calculate the bandstructure of lead and its electronic density of states from first principles. The results of the calculation agree with optical and specific heat data to within 30 and 1% respectively. Calculated frequencies for the second band hole surface agree with experimental Fermi surface results to within 4%. An application of the bandstructure results to the study of the electron-phonon interaction and superconductivity is made including the variation of these properties upon alloying lead with bismuth. These results are also in good agreement with experiment and demonstrate the increase of the superconducting transition temperature for the Pb-Bi alloys

Ab initio bandstructure of lead

The self-consistent semi-relativistic APW method has been employed to calculate the bandstructure of lead and its electronic density of states from first principles. The results of the calculation agree with optical and specific heat data to within 30 and 1% respectively. Calculated frequencies for the second band hole surface agree with experimental Fermi surface results to within 4%. An application of the bandstructure results to the study of the electron-phonon interaction and superconductivity is made including the variation of these properties upon alloying lead with bismuth. These results are also in good agreement with experiment and demonstrate the increase of the superconducting transition temperature for the Pb-Bi alloys

FOCUSING OF DISPERSIVE PHONONS IN Ge

Singularities in the phonon flux are observed and calculated for dispersive phonons in Ge

Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals. © 2016 Elsevier B.V