Multi-orbital Non-Crossing Approximation from maximally localized Wannier functions: the Kondo signature of copper phthalocyanine on Ag (100)

We have developed a multi-orbital approach to compute the electronic structure of a quantum impurity using the non-crossing approximation. The calculation starts with a mean-field evaluation of the system's electronic structure using a standard quantum chemistry code. Here we use density functional theory (DFT). We transformed the one-electron structure into an impurity Hamiltonian by using maximally localized Wannier functions (MLWF). Hence, we have developed a method to study the Kondo effect in systems based on an initial one-electron calculation. We have applied our methodology to a copper phthalocyanine molecule chemisorbed on Ag (100), and we have described its spectral function for three different cases where the molecule presents a single spin or two spins with ferro- and anti-ferromagnetic exchange couplings. We find that the use of broken-symmetry mean-field theories such as Kohn-Sham DFT cannot deal with the complexity of the spin of open-shell molecules on metal surfaces and extra modeling is needed

Utilizing of furnace waste heat for hot water production

Obsah bakalářské práce pojednává o možnostech využití odpadního tepla spalin žíhací pece pro ohřev teplé užitkové vody. V kapitolách jsou popsány jednotlivé druhotné energetické zdroje, výměníky tepla, jejich rozdělení, typy a konstrukce. Podrobněji se věnuje výpočtu výměníku tepla spaliny-voda pro ohřev teplé užitkové vody podle zadaných parametrů. V závěru bakalářské práce je uvedeno technicko-ekonomické zhodnocení a porovnání se současným stavem.The content of bachelor thesis deals with utilizing of furnace waste heat for hot water production. In the chapters are described various types of secondary energy sources, heat exchangers their distribution, types and their design. More detail is devoted to the calculation of the heat exchanger combustion water for heating hot water in accordance with the parameters. In conclusion of study is given technical and economic evaluation and compared to the status quo.

Many-body effects in magnetic inelastic electron tunneling spectroscopy

Magnetic inelastic electron tunneling spectroscopy (IETS) shows sharp increases in conductance when a new conductance channel associated to a change in magnetic structure is open. Typically, the magnetic moment carried by an adsorbate can be changed by collision with a tunneling electron; in this process the spin of the electron can flip or not. A previous one-electron theory [Phys. Rev. Lett. {\bf 103}, 176601 (2009)] successfully explained both the conductance thresholds and the magnitude of the conductance variation. The elastic spin flip of conduction electrons by a magnetic impurity leads to the well known Kondo effect. In the present work, we compare the theoretical predictions for inelastic magnetic tunneling obtained with a one-electron approach and with a many-body theory including Kondo-like phenomena. We apply our theories to a singlet-triplet transition model system that contains most of the characteristics revealed in magnetic IETS. We use two self-consistent treatments (non-crossing approximation and self-consistent ladder approximation). We show that, although the one-electron limit is properly recovered, new intrinsic many-body features appear. In particular, sharp peaks appear close to the inelastic thresholds; these are not localized exactly at thresholds and could influence the determination of magnetic structures from IETS experiments.Analysis of the evolution with temperature reveals that these many-body features involve an energy scale different from that of the usual Kondo peaks. Indeed, the many-body features perdure at temperatures much larger than the one given by the Kondo energy scale of the system.Comment: 10 pages and 6 figure

Elastic transport through dangling-bond silicon wires on H passivated Si(100)

We evaluate the electron transmission through a dangling-bond wire on Si(100)-H (2x1). Finite wires are modelled by decoupling semi-infinite Si electrodes from the dangling-bond wire with passivating H atoms. The calculations are performed using density functional theory in a non-periodic geometry along the conduction direction. We also use Wannier functions to analyze our results and to build an effective tight-binding Hamiltonian that gives us enhanced insight in the electron scattering processes. We evaluate the transmission to the different solutions that are possible for the dangling-bond wires: Jahn-Teller distorted ones, as well as antiferromagnetic and ferromagnetic ones. The discretization of the electronic structure of the wires due to their finite size leads to interesting transmission properties that are fingerprints of the wire nature

Current-induced mechanical torque in chiral molecular rotors

A great endeavor has been undertaken to engineer molecular rotors operated by an electrical current. A frequently met operation principle is the transfer of angular momentum taken from the incident flux. In this paper we present an alternative driving agent that works also in situations where angular momentum of the incoming flux is conserved. This situation arises typically with molecular rotors that exhibit an easy axis of rotation. For quantitative analysis we investigate here a classical model, where molecule and wires are represented by a rigid curved path. We demonstrate that in the presence of chirality the rotor generically undergoes a directed motion, provided that the incident current exceeds a threshold value. Above threshold, the corresponding rotation frequency (per incoming particle current) for helical geometries turns out to be $2\pi m/M_1$, where $m/M_1$ is the ratio of the mass of an incident charge carrier and the mass of the helix per winding number

Optimization of four-bar mechanism geometry for the predescribed trajectory

Práce se zabývá optimalizací délek ramen čtyřčlenného mechanismu typu RRRR pomocí maticové kinematiky. Srovnává a popisuje metody k tomu dostupné v prostředí MATLAB. Dále je navržen optimalizační algoritmus, využívající funkci fminsearch, pro niž realizuje prvotní odhad algoritmus Monte-Carlo. Pro navržený algoritmus jsou definovány základní požadavky na trajektorii, kterou je možno přesně kopírovat.This thesis deals with the optimization of arm lengths of four-bar RRRR mechanism using matrix kinematics. It compares and describes the methods, which are available in MATLAB software environment for this purpose. Consequently, an optimization algorithm using fmincon function is designed for which Monte-Carlo algorithm performs the first estimates. Elementary requirements for the proposed algorithm are devised in order to accurately duplicate the predescribed trajectory.

Chirality-controlled spin scattering through quantum interference

Chirality-induced spin selectivity has been reported in many experiments, but a generally accepted theoretical explanation has not yet been proposed. Here, we introduce a simple model system of a straight cylindrical free-electron wire, containing a helical string of atomic scattering centers, with spin-orbit interaction. The advantage of this simple model is that it allows deriving analytical expressions for the spin scattering rates, such that the origin of the effect can be easily followed. We find that spin-selective scattering can be viewed as resulting from constructive interference of partial waves scattered by the spin-orbit terms. We demonstrate that forward scattering rates are independent of spin, while back scattering is spin dependent over wide windows of energy. Although the model does not represent the full details of electron transmission through chiral molecules, it clearly reveals a mechanism that could operate in chiral systems.Comment: 7 pages, 4 figure

Waste heat recovery vith steam turbine

Cílem této diplomové práce je návrh spalovny komunálního odpadu s využitím vyrobené páry pro výrobu elektrické energie a distribuci tepla. V úvodu se zabývá vývojem problematiky odpadů a současným stavem odpadového hospodářství. V další části jsou popsány možnosti zpracování odpadů a možných řešení současného stavu odpadové problematiky. Koncepce spalování odpadu: Pro spalování odpadu je použita linka spalující 100 000 tun komunálního odpadu ročně. Spalování probíhá v roštovém kotli. Jeho výhodou je univerzálnost a flexibilita k odpadu. Výroba elektrické energie je řešena kondenzační turbínou s regulovaným odběrem. Čištění spalin je navrženo polo-mokrou metodou. Finální fáze zahrnuje bilanční výpočet, výpočet vyrobené elektrické energie a základní ekonomické vyhodnocení.The aim of this thesis is the design of municipal waste incinerator using the generated steam for power generation and distribution of heat. At the beginning is engaged in development of waste issues and the current state of waste management. The next section describes the options of waste treatment and possible solutions to the current state of waste issues. The concept of waste incineration plants: For waste incineration is used line for burning 100,000 tons of municipal waste per year.Combustion takes place in a grate boiler. Its advantage is the versatility and flexibility to waste. Electricity generation is dealt with condensing turbine with controlled consumption. The flue gas cleaning is designed to semi-wet method. The final stage involves the calculation of the balance, the calculation of electric energyand basic economic evaluation.

Band selection and disentanglement using maximally-localized Wannier functions: the cases of Co impurities in bulk copper and the Cu (111) surface

We have adapted the maximally-localized Wannier function approach of [I. Souza, N. Marzari and D. Vanderbilt, Phys. Rev. B 65, 035109 (2002)] to the density functional theory based Siesta method [J. M. Soler et al., J. Phys.: Cond. Mat. 14, 2745 (2002)] and applied it to the study of Co substitutional impurities in bulk copper as well as to the Cu (111) surface. In the Co impurity case, we have reduced the problem to the Co d-electrons and the Cu sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined density functional parameters in a fully orthonormal basis set. In order to test the quality of the Wannier approach to surfaces, we have studied the electronic structure of the Cu (111) surface by again transforming the density functional problem into the Wannier representation. An excellent description of the Shockley surface state is attained, permitting us to be confident in the application of this method to future studies of magnetic adsorbates in the presence of an extended surface state