2.6M - 1. Institut für Theoretische Physik - Universität Stuttgart

Abstract
Atomic data of atoms and ions in intensive neutron star magnetic fields are important for
interpreting thermal spectra of neutron stars. These spectra are measured with spacebased
X-ray observations (e.g. by the Chandra satellite). The solution of Schrödinger’s
equation via Hartree-Fock equations in adiabatic approximation solved with the finite
element method and B-spline interpolation yields only approximate energy eigenvalues.
Ground state energy values are improved by applying the Diffusion Quantum Monte
Carlo method. A simulation technique is used by introducing walkers guided in 3N
dimensional space. The transformation of the time-dependent Schrödinger equation
to imaginary time leads to a diffusion equation describing both propagation and creation/annihilation
(branching) of the walkers. The walker underlie the influence of the
quantum force and perform a random walk. A central role of the simulation technique
is played by the guiding wavefunction. The Hartree-Fock wavefunction in adiabatic approximation
multiplied by a Jastrow-Factor is used as the guiding wavefunction. In this
thesis the Variational Quantum Monte Carlo method, the fixed-phase and the releasedphase
Diffusion Quantum Monte Carlo method are applied. The Diffusion Quantum
Monte Carlo method yields, by taking the average of the local energies at the walker
positions, the desired ground state energy. The CPU time increases rapidly with growing
number of electrons. Therefore the simulation is carried out on a computer cluster
of the ”High Performance Computing Center Stuttgart”. The calculated values are the
most comprehensive and accurate ground state energies of medium-Z atoms up to iron
(Z = 26) in neutron star magnetic fields presented in literature so far.
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