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Description of narrow resonances using two-potential formula
Bednařík, Lukáš ; Čížek, Martin (advisor) ; Houfek, Karel (referee)
In the presented thesis we study tunneling problems with projection formalism and two potential approach. We apply this approximative method proposed by S.A. Gurvitz in [4] to two new potentials with a quasistationary state. In the next chapter we generalize this method to one-dimensional nonsymmetric potential. A new formula is found and used for calculation of energy width. We compare our results with a numerical method of complex scaling. Finally, we discuss three-dimensional potential. One axis of symmetry is assumed and we derive relatively simple formula for energy width.
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Průchod proudu vibrujícím molekulárním můstkem
Šmít, Daniel ; Čížek, Martin (advisor) ; Novotný, Tomáš (referee)
In the present work we study transmission of electron through vibrat- ing molecular junction interacting with leads using a method of nonequilibrium Green functions. Our Green functions use combination of first quantization to treat vibrational levels and second quantization to treat electron processes. We treat the change of vibrational potential of junction induced by charging of junc- tion, we find a spectral function and a magnitude of current through the junction. We confirm the effect of Fermi sea and Frack-Condon factors on sharpening of peaks. We study these processes on model motivated by biphenyl molecule, in- troducing double well potential and study an effect of quasidegenerate energy levels. We present the shift of peaks, resulting from an increase of moment of inertia, to positions determined by Franck-Condon factors.
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Interaction of electrons with vibrating molecules: molecular electronic applications
Pshenichnyuk, Ivan ; Čížek, Martin (advisor) ; Lipavský, Pavel (referee) ; Thoss, Michael (referee)
Interaction of electrons with vibrating molecules: molecular electronics applications Ivan A. Pshenichnyuk Submitted for the degree of Doctor of Philosophy October 2010 Abstract Interaction of the electric current, flowing through the molecular junction, with the internal vibrations of the bridging molecule is investigated. Two different theo- retical approaches which allow us to calculate the current and other characteristics of the junction are compared. The first method is based on the scattering theory and Landauer formula, and the second on the Wangsness-Bloch-Redfield master equa- tion technique. A set of original models of the molecular bridge with anharmonic vibrational mode and asymmetric coupling to the leads is formulated. Influence of anharmonic vibrations and different types of symmetry in the junction on the current-voltage dependencies of the bridge are discussed. As an example of the phenomenon, which can only be found beyond the harmonic approximation, we demonstrate the existence of the so called "motor effect", i. e. the strong depen- dence of the average angular momentum of the molecule on the voltage, applied across the junction. The key parameters, responsible for the effect appearance, such as the rotational barrier height and the symmetry in the junction are discussed.
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Phaseshift analysis
Strnad, Otto ; Horáček, Jiří (advisor) ; Čížek, Martin (referee)
Nazev prace; Fazova analyza Autor: Otto Strnad Katedra (ustav): tfstav teorcticke fyziky, Matematicko-fyzikalni fakulta, Univer- zita Karlova v Praze Vedoucf bakalafske prace: prof. RNDr. Jin Horacek, DrSc. e-mail vedouciho: Jiri.Horacek@mff.cuni.cz Abstrakt: V pfedlozene praci studujeme vlastnosti statisticke Fade aproximace (Fade typu III) a pouzfvame Fade aproximaci k vypoctu delky rozptylu, sfrky rezonance a k simulaci analyzy fazoveho posuvu pfi nerelativistickem rozptylu. Provedeni iterativni linearizovane metody vyvinute pro konstrukci Fade aproxi- mace typu III je detailne testovano na simulovanych datech odvozenych pomoci dvou modelovych funkci, Metoda vykazuje vehni ryclilou konvergenci. Metoda je pouzita k vypoctu delky rozptylu, pro nizkoenergeticky elasticky rozptyl elek- tronu na atomech helia, neonu a argonu aje porovnana s publikovanymi vyslcdky. Je vypo6'tana sifka rezonance pro nejnizsf S rezonance pro rozptyl e 4- He+ a po- rovnana s vysledky prezentovanymi v [1], Je provedena analyza fazoveho posuvu pomoci Fade aproximace typu III nerelativistickeho rozptylu na simulovanych datech. Pocftacovy kod vjazyku C realizujici aproximaci Fade III je prezentovan se svym strucnym u^ivatelskym rnanualem a specifikacf vstupu a vystupu. Klicova slova: Pade aproximace, delka rozptylu, ...
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Few-Body Systems with Non-Zero Strangeness
Donoval, Jan ; Mareš, Jiří (advisor) ; Čížek, Martin (referee)
In this work, we studied the Kd scattering length. We formulated the Faddeev equations in the AGS form for the Kd system. We performed three-body Faddeev calculations in the s-wave approximation in the isospin basis. We studied the sensitivity of the Kd scattering length on the two-body inputs. Our results are reasonably close to the values of previous calculations.
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