|dc.description.abstract||Extended aqueous systems, crystalline ice and liquid water, are studied computationally
to investigate their ground state and excited state properties.
Methods from solid state physics and quantum chemistry are combined to
shed light on some of the unusual properties of water and ice.
For the ground state of crystalline ice, density functional theory (DFT) calculations
are compared to an ab initio incremental ansatz that utilizes periodic
Hartree-Fock together with localized electron correlation calculations.
It is shown that the many-body decomposition of the electron correlation
converges very fast, allowing the achievement of excellent agreement with
experimental data even when limiting correlation energy contributions to
two-body terms only. The incremental method is utilized by a computer program
that combines the periodic and localized calculations, and allows for
structural optimization of the system of interest.
The adsorption of water molecules on the surface of ice is studied using DFT.
Adsorption is found to be favoured on non-crystallographic adsorption sites,
and a slight tendency towards the formation of rough surfaces is reported.
The localization of excess electrons at the surface of ice is facilitated by coadsorbed
water molecules. For a correct theoretical description of the latter,
a self-interaction correction scheme for the excess electron has to be used.
However, it is sufficient to limit the self-interaction correction to the excess
electron only, since the neutral ice surface itself is well described within conventional
DFT. The self-interaction correction scheme is incorporated into a
commonly used DFT program package.
Optical excitations of crystalline ice are calculated using many-body perturbation
theory. Solving the two-particle Bethe-Salpeter equation yields optical
spectra in excellent agreement with experimental data. Based on this
agreement, an embedding model is developed that reduces the hydrogen
bond network to its most important contribution. The model is applied to
crystalline ice, where it reproduces the experimental spectral features, and to
microscopic liquid water structures obtained from molecular dynamics simulations,
where it reproduces the energy shift of the first absorption peak and
gives overall good agreement with experiment. The driving force of water’s
anomalous optical behaviour is identified.||en_US