My research involves computer simulations of liquids, solids and surfaces. To study the atomic structure and dynamics of these different systems I use a range of different simulation techniques. Molecular dynamics (MD) is a useful tool for studying systems at finite temperature in different thermodynamical ensembles, density functional theory (DFT) can be used to calculate the electronic structure of materials and can be connected to MD simulations, and the adaptive kinetic Monte Carlo (AKMC) method can be used to study the time evolution of systems on time-scales much larger than those accessible via MD simulations. To study interesting quantum effects like quantum tunneling I use path-integral MD (PIMD) simulations. I also calculate various spectroscopic properties from the computer models. For example, both x-ray spectroscopies (XAS, EXAFS) and nuclear magnetic resonance (NMR) spectra can be calculated using theoretical methods and by comparing directly to experimental measurements more can be learned about the system under study.
Liquid water and ice
Water and ice pervade our environment and play a major role in a vast range of natural processes. However, these everyday substances still hold many secrets that keep scientists busy. If we can understand better what happens on a molecular level in both water and ice, it would have large implications in a wide range of disciplines, from biology and clean-energy technologies to environmental sciences and astrochemistry.
As an interesting example, ice is ubiquitous in interstellar space where it is usually found in an amorphous solid phase on dust particles in interstellar molecular clouds. Surfaces of such amorphous ice particles act as catalytic centers for the formation of many molecules in space, including biologically interesting molecules that may actually have something to do with the emergence of life on Earth. I am interested in understanding the mechanisms of such chemical processes and how the growth, morphology and intermolecular structure of interstellar amorphous ice influences the chemical reactivity.
Surface diffusion and quantum tunneling
The adsorption and diffusion of atoms and molecules on metal surfaces are microscopic processes that are both interesting from a fundamental point of view and important to various technologies, for example in heterogeneous catalysis and hydrogen fuel cells. Many questions still remain unanswered about surface adsorption and diffusion. By studying simple model systems, like H atoms on well-defined transition metal surfaces, one can compare theoretical simulations to experiments and gain insights into general mechanisms in surface diffusion. In my work I have focused on topics related to the quantum mechanical behavior of the H atom, i.e. the ability of H to delocalize on the surface and tunnel through energy barriers.
Hydrogen bonded ferroelectrics
Ferroelectricity is a collective phenomenon leading to the emergence of an electric polarization in materials. External electric fields can be used to control the direction and magnitude of the electric response, and this has a range of useful practical applications, including in optoelectronic devices, temperature sensors and switchable memories. Most ferroelectric materials known today are inorganic compounds, but there has recently been a surge in interest in biological, hydrogen (H) bonded materials as potential low-cost, environmentally friendly ferroelectrics. These systems have many uniquely interesting properties due to the role of collective motion of protons along H-bonding chains and the large impact of nuclear quantum effects. Furthermore, the ferroelectric-paraelectric (order-disorder) phase transition is not completely understood. My work aims to deepen our fundamental understanding of collective H-bond dynamics, its role in ferroelectric-paraelectric phase transitions, and the impact of quantum effects by using state-of-the-art simulation methods.