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Dissertation
Electron-Nuclear Correlation in Laser-Driven Diatomic Molecules
(2011-12-19)
The interaction of short intense laser pulses with atoms/molecules produces a multitude of highly nonlinear processes requiring a non-perturbative treatment. Detailed study of these highly nonlinear processes by numerically solving the time-dependent Schrodinger equation becomes a daunting task when the number of degrees of freedom is large. Also the coupling between the electronic and nuclear degrees of freedom further aggravates the computational problems. In the present work we show that the time-dependent Hartree ...
Dissertation
Non-Born-Oppenheimer Dynamics of Hydrogen Molecules in Strong Laser-Fields
(2009-05-14)
Die Arbeit behandelt die numerische Untersuchung von Wasserstoff-Moleküldynamik in starken Laserfeldern. Im Speziellen wird die Struktur von Ionisationsspektren bei Einfach-Photoionisation betrachtet. Korrelationen zwischen Elektron- und Kernbewegung werden identifiziert und mit Effekten in den Energiespektren in Verbindung gebracht. Dabei wird stets auf die Integration der zeitabhängigen Schrödingergleichung zurückgegriffen.
Aufsatz
Delocalization of a hole in van der Waals clusters: Ionization potential of rare-gas and small Hg_n clusters
(American Physical Society, 1993)
The size dependence of the ionization potential I_p(n) of van der Waals (vdW) bound clusters has been calculated by using a model Hamiltonian, which includes electron hopping, vdW interactions, and charge-dipole interactions. The charge-density and dipole-density distributions for both neutral and ionized n-atom clusters are determined self-consistently. The competition between the polarization energy of the neutral atoms surrounding a partially localized hole and the tendency toward hole delocalization in the ionized ...
Aufsatz
Squeezed thermal phonons precurse nonthermal melting of silicon as a function of fluence
(2013)
A femtosecond-laser pulse can induce ultrafast nonthermal melting of various materials along pathways
that are inaccessible under thermodynamic conditions, but it is not known whether there is any structural
modification at fluences just below the melting threshold. Here, we show for silicon that in this regime the
room-temperature phonons become thermally squeezed, which is a process that has not been reported
before in this material. We find that the origin of this effect is the sudden femtosecond-laser-induc ...
Aufsatz
Theoretical study of the structural dependence of nuclear quadrupole frequencies in high-T_c superconductors
(American Physical Society, 1989)
The remarkable difference between the nuclear quadrupole frequencies v_Q of Cu(1) and Cu(2) in YBa_2Cu_3O_6 and YBa_2Cu_3O_7 is analyzed. We calculate the ionic contribution to the electric field gradients and estimate, by using experimental results for Cu_2O and La_2CuO_4, the contribution of the d valence electrons. Thus, we determine v_Q1, v_Q2, and the asymmetry parameter η for YBa_2Cu_3O_6 and YBa_2Cu_3O_7. The number of holes in dthe Cu-O planes and chains is found to be important for the different behavior of ...
Aufsatz
Theory for the Photoacoustic Response to X-Ray Absorption
(American Physical Society, 1988)
A microscopic theory is presented for the photoacoustic effect induced in solids by x-ray absorption. The photoacoustic effect results from the thermalization of the excited Auger electrons and photoelectrons. We explain the dependence of the photoacoustic signal S on photon energy and the proportionality to the x-ray absorption coefficient in agreement with recent experiments on Cu. Results are presented for the dependence of S on photon energy, sample thickness, and the electronic structure of the absorbing solid.
Aufsatz
Theory for Optical Absorption in Small Clusters: Dependence on Atomic Structure and Cluster Size
(American Physical Society, 1994)
We present a theory which permits for the first time a detailed analysis of the dependence of the absorption spectrum on atomic structure and cluster size. Thus, we determine the development of the collective excitations in small clusters and show that their broadening depends sensitively on the tomic structure, in particular at the surface. Results for Hg_n^+ clusters show that the plasmon energy is close to its jellium value in the case of spherical-like structures, but is in general between w_p/ \wurzel{3} and ...
Aufsatz
Transport properties of one-dimensional, disordered two-band systems
(The Institute of Physics, London, 1986)
We have studied the transport properties of disordered one-dimensional two-band systems. The model includes a narrow d band hybridised with an s band. The Landauer formula was used in the case of a very narrow d band or in the case of short chains. The results were compared with the localisation length of the wavefunctions calculated by the transfer matrix method, which allows the use of very lang chains, and an excellent agreement was obtained.
Aufsatz
Relativistic calculations of atomic structure
(1984)
A review of relativistic atomic structure calculations is given with a emphasis on the Multiconfigurational-Dirac-Fock method. Its problems and deficiencies are discussed together with the contributions which go
beyond the Dirac-Fock procedure.
Aufsatz
Relativistic many-electron SCF correlation diagram for superheavy quasimolecules: Pb - Pb
(1981)
We present the first relativistic many-electron SCF correlation diagram for a superheavy quasimolecule: Pb - Pb. The discussion shows a large number of quantitative as well as qualitative differences as compared with the known one-electron correlation diagram.