Halle, Univ., Naturwissenschaftliche Fakultät II, Diss., 2009. / Tag der Verteidigung: 15.04.2009.

Techn. Universiẗat, Diss., 1998--Dresden.

Ab initio calculations of the electronic structure of freestanding Cu and Na nanowires with a diameter of few atoms are presented. The calculations are based on density functional theory in local density approximation using a Screened Korringa-Kohn-Rostoker-Green's function method. The method was extended for the description of quasi-onedimensional systems. Translational invariance in direction of the wire is assumed. The dependence of the bandstructure and the density of states from thickness and shape of the cross-section is discussed. The quantum confinement of the eigenstates is analysed. By comparing the results of the Na and Cu wires, the influence of the d-electrons is shown. Based on the Landauer theory of transport the conductance is obtained within a Green's function formalism. The numerical description of the conductance is tested for ideal translationally invariant Na and Cu wires. The influence of substitutional transition metal impurities on the electronic structure and the conductance of the 2x2 Cu wire is studied. A spin-dependent discussion is given for magnetic impurities. / Es werden ab initio Berechnungen der elektronischen Struktur freistehender Na- und Cu-Nanodrähte mit einem Durchmesser von wenigen Atomen präsentiert. Für die Berechnung wird eine Screened Korringa-Kohn-Rostoker-Grennsche Funktionsmethode genutzt, die auf der Spindichtefunktionaltheorie in lokaler-Spindichtenäherung basiert. Diese Methode wurde für die Beschreibung von quasieindimensionalen Systemen erweitert. Die Drähte werden als translationsinvariant in Drahtrichtung beschrieben. Es wird die Abhängigkeit der Bandstruktur und der Zustandsdichte von der Dicke und der Form des Querschnitts diskutiert. Das Quantenconfinement der Eigenzustände wird analysiert. Durch den Vergleich der Resultate für den Na- und den Cu-Draht kann der Einfluss der d-Elektronen gezeigt werden. Ausgehend von der Landauer-Theorie des Transports wird der Leitwert im Rahmen eines Greenschen Funktions-Formalismus berechnet. Diese neue numerische Beschreibung des Leitwertes wird an idealen translationsinvarianten Drähten getestet. Es wird der Einfluss von substitutionellen 3d-Übergangsmetall-Störungen auf die elektronische Struktur und auf den Leitwert von 2x2-Cu-Drähten studiert. Im Fall magnetischer Defekte wird dieser Einfluss spinabhängig diskutiert.

Techn. Universiẗat, Diss., 2002--Dresden.

Ab initio calculations of the electronic structure of freestanding Cu and Na nanowires with a diameter of few atoms are presented. The calculations are based on density functional theory in local density approximation using a Screened Korringa-Kohn-Rostoker-Green's function method. The method was extended for the description of quasi-onedimensional systems. Translational invariance in direction of the wire is assumed. The dependence of the bandstructure and the density of states from thickness and shape of the cross-section is discussed. The quantum confinement of the eigenstates is analysed. By comparing the results of the Na and Cu wires, the influence of the d-electrons is shown. Based on the Landauer theory of transport the conductance is obtained within a Green's function formalism. The numerical description of the conductance is tested for ideal translationally invariant Na and Cu wires. The influence of substitutional transition metal impurities on the electronic structure and the conductance of the 2x2 Cu wire is studied. A spin-dependent discussion is given for magnetic impurities. / Es werden ab initio Berechnungen der elektronischen Struktur freistehender Na- und Cu-Nanodrähte mit einem Durchmesser von wenigen Atomen präsentiert. Für die Berechnung wird eine Screened Korringa-Kohn-Rostoker-Grennsche Funktionsmethode genutzt, die auf der Spindichtefunktionaltheorie in lokaler-Spindichtenäherung basiert. Diese Methode wurde für die Beschreibung von quasieindimensionalen Systemen erweitert. Die Drähte werden als translationsinvariant in Drahtrichtung beschrieben. Es wird die Abhängigkeit der Bandstruktur und der Zustandsdichte von der Dicke und der Form des Querschnitts diskutiert. Das Quantenconfinement der Eigenzustände wird analysiert. Durch den Vergleich der Resultate für den Na- und den Cu-Draht kann der Einfluss der d-Elektronen gezeigt werden. Ausgehend von der Landauer-Theorie des Transports wird der Leitwert im Rahmen eines Greenschen Funktions-Formalismus berechnet. Diese neue numerische Beschreibung des Leitwertes wird an idealen translationsinvarianten Drähten getestet. Es wird der Einfluss von substitutionellen 3d-Übergangsmetall-Störungen auf die elektronische Struktur und auf den Leitwert von 2x2-Cu-Drähten studiert. Im Fall magnetischer Defekte wird dieser Einfluss spinabhängig diskutiert.

Im Rahmen der vorliegenden Arbeit wird eine Tight-Binding-Formulierung der Korringa-Kohn-Rostoker-Greenschen-Funktionsmethode vorgestellt. Dabei werden mittels eines geeignet gewählten Referenzsystems abgeschirmte Strukturkonstanten konstruiert. Es werden die Vorteile und Grenzen dieser Transformation des Formalismus diskutiert. Es wird gezeigt, daß der numerische Aufwand zur erechnung der Elektronenstruktur von Systemen mit langgestreckter Elementarzelle linear mit der Systemgröße wächst. Damit ist eine Behandlung von Systemen mit 500 und mehr Atomen pro Elementarzelle möglich. Anhand von umfangreichen Testrechnungen kann demonstriert werden, daß das neue Verfahren bezüglich seiner Genauigkeit mit dem traditionellen KKR-Verfahren vergleichbar ist. Es werden Anwendungen zur Berechnung der Elektronenstruktur sowie zur Zwischenlagenaustauschkopplung von Co/Cu(100)-Vielfachschichten vorgestellt. / A newly developed ab initio tight-binding-formulation of the Korringa-Kohn-Rostoker-Green's function method for layered systems is presented. Screened structure constants are calculated by means of a repulsive reference system. Advantages and limits of this transformation of the formalism are discussed in detail. The numerical effort for self consistent electronic structure calculations of systems with a large prolonged supercell scales linearly with the system size. Systems with up to 500 atoms per unit cell can be treated easily. The accuracy of the new method is of the same order as the traditional KKR method. Applications to electronic structure calculations and magnetic interlayer exchange coupling in Co/Cu(100) multilayers are presented.

Koldioxidutsläppen i världen orsakar stora miljöförstöringar och byggbranschen står för en stor del av utsläppen. Samtidigt som utsläppen behöver minska finns ett behov av att bygga fler idrottshallar i Sverige. Utöver det behöver även kostnaderna hållas så låga som möjligt. Därför syftar denna studie till att klargöra hur stor skillnaden i pris och koldioxidutsläpp är beroende på val av pelare i ett verkligt fall. De pelare som undersökts och jämförts är varmformade konstruktionsrör (VKR), kallformade konstruktionsrör (KKR) och energisnåla kallformade konstruktionsrör (Zero KKR). För att genomföra studien dimensionerades pelare till en idrottshall enligt europeiska standarder, så kallade Eurokoder. Dimensioneringen utgick från stålleverantören Tibnors sortiment. Information om pris och koldioxidutsläpp för de dimensioner som togs fram samlades in från Tibnor och dess återförsäljare. En sammanställning av informationen gjordes i tabeller och diagram för jämförelse. Resultatet visar att det totala priset för pelare till idrottshallen är 20,7% lägre vid val av KKR istället för VKR. Jämförelsen visar även att det går att göra en utsläppsbesparing på 8,7% genom att, genomgående, välja KKR istället för VKR till pelare för den idrottshall som undersökts. Med Zero KKR skulle det vara möjligt att minska koldioxidutsläppen pelarna till idrottshallen orsakar med ytterligare 66,8% och slutsatsen kan dras att användning av Zero KKR alltid skulle bidra till en markant minskning av koldioxidutsläppet. / Carbon dioxide emissions worldwide cause significant environmental damage and the construction industry is responsible for many of these emissions. At the same time that emissions need to be reduced, there is a need to build more sports halls in Sweden. In addition, costs also need to be kept down. Therefore, this study aims to clarify how big the difference in price and carbon dioxide emissions is depending on the choice of columns in a real case. The colums that has been investigated and compared is Hot-Formed Hollow Sections, Cold-Formed Hollow Sections and the energy efficient Zero Cold-Formed Hollow Sections. To do the investigation, columns for a sports hall were dimensioned according to European standards, so-called Eurocodes. Dimensioning was based on the steel supplier Tibnor's range. Data regarding price and carbon dioxide emissions for the dimensions produced were collected from Tibnor and its dealers. A compilation was made in tables and charts for comparison. The result shows that the total price for the columns to the sportshall is 20,7% lower for Cold-Formed Hollow Sections than Hot-Formed Hollow Sections. The comparison also shows that it is possible to save 8.7% on emissons by consistently choosing Cold-Formed Hollow Section instead of Hot-Formed Hollow Sections as pillars for the investigated sports hall. With Zero Cold-Formed Hollow Sections, it would be possible to reduce the carbon dioxide emissions for the columns of the sports hall by a further 66.8% and the conclusion can be drawn that using Zero Cold-Formed Hollow Sections would always contribute to a significant reduction in carbon dioxide emissions.

The aim of this thesis is description and understanding of private equity industry as a part of alternative asset class. In the first part, we describe the basic concepts of private equity industry and characteristics of individual subjects present in this sector. Analysis of the industry and basic comparison of private equity in Europe and United States is the theme of the second part of this paper. The base of knowledge created in the previous parts supports the analysis of buyouts and their value creation strategies. On the example of Kohlberg Kravis Roberts, pre-eminent private equity firm, we show how private equity works in practice and what current trends in the industry are. In the end, we estimate the subjective value of one unit of ownership in KKR and list that risks could affect the company and the industry.

<p>The interplay between magnetism and structure has been studied in magnetic multilayers by electronic structure calculations based on density functional theory and analyzed in terms of models. The main ideas behind the Korringa-Kohn-Rostocker Green’s function method are described and the implementation of the coherent potential approximation is outlined.</p><p>A simple model for the bilinear magnetic interlayer coupling in metallic multilayers is derived that elucidates the main characteristics of the effect such as coupling period and origin of damping. An analysis of two exotic effects on the magnetic interlayer coupling, Fermi surface nesting and magnetic enhancement is also performed. The Fermi surface nesting in CuPd for the (110) direction is shown to induce a sharp peak in the magnetic interlayer coupling amplitude for a Fe/CuPd/Fe system when the Cu concentration is 60% in the CuPd alloy. The high magnetic susceptibility in Pd is shown to have strong influence on the magnetic interlayer coupling in a Fe/Pd/Fe (100) system where it changes the amplitude, phase and induces an offset.</p><p>The relation between surface structure and magnetic properties in metallic multilayers is investigated in terms of a theory that is based on a symbiosis between experiment and theory. By calculating the total magnetic moment of a sample for a large range of possible interface structures and comparing to experimental results for equivalent samples a parameter that describes the interface structure is determined. This parameter is then shown to be universal for the particular combination of elements in the structure both as regards the calculated total magnetic moment as well as the magnetic interlayer coupling and the critical temperatures. </p>

The interplay between magnetism and structure has been studied in magnetic multilayers by electronic structure calculations based on density functional theory and analyzed in terms of models. The main ideas behind the Korringa-Kohn-Rostocker Green’s function method are described and the implementation of the coherent potential approximation is outlined. A simple model for the bilinear magnetic interlayer coupling in metallic multilayers is derived that elucidates the main characteristics of the effect such as coupling period and origin of damping. An analysis of two exotic effects on the magnetic interlayer coupling, Fermi surface nesting and magnetic enhancement is also performed. The Fermi surface nesting in CuPd for the (110) direction is shown to induce a sharp peak in the magnetic interlayer coupling amplitude for a Fe/CuPd/Fe system when the Cu concentration is 60% in the CuPd alloy. The high magnetic susceptibility in Pd is shown to have strong influence on the magnetic interlayer coupling in a Fe/Pd/Fe (100) system where it changes the amplitude, phase and induces an offset. The relation between surface structure and magnetic properties in metallic multilayers is investigated in terms of a theory that is based on a symbiosis between experiment and theory. By calculating the total magnetic moment of a sample for a large range of possible interface structures and comparing to experimental results for equivalent samples a parameter that describes the interface structure is determined. This parameter is then shown to be universal for the particular combination of elements in the structure both as regards the calculated total magnetic moment as well as the magnetic interlayer coupling and the critical temperatures.