Nowadays first-principles methods enable quantitive and qualitative description of complex materials. Based on quantum mechanics and numerical methods, they are widely applied to study structural,
electronic, magnetic, transport and optical properties of condensed matter without or almost without adjustable parameters.

In my talk I’ll present one of such approaches, based on the multiple scattering theory using a Green function formalism. This method is designed to study bulk materials, surfaces, interfaces, clusters and alloys.
The main focus of our activity is magnetism and I’ll show most prominent examples of our research in this field. After a very short introduction about the method, we use, I’ll discuss how theoretical simulations of XAS & XMCD
spectra can help to obtain adequate information about the chemical composition, structural, electronic and magnetic properties of complex materials such as magnetic oxides and otological insulators.

In the second part of my talk, I’ll present a first-principles formalism to study spin waves. Spin waves or magnons are collective magnetic excitations, which provide important information about magnetic properties of solids.
Apparently, magnons participate in many physical phenomena such as superconductivity, domain wall motion, spin Seebeck effect etc. They can be described as quasiparticles of a certain wave vector and of a certain energy.
The wave vector and the energy are linked together by a characteristic dispersion relation. Spin waves can be studied with several experimental techniques such as ferromagnetic resonance, Brillouin light scattering,
neutron scattering, scanning tunnelling and spin polarised electron energy loss spectroscopy.
Thereby, spin waves can be described theoretically using either a macroscopic phenomenological model or a microscopic treatment of solids. In my talk, I’ll present a first-principles approach to calculate spin waves in complex
systems such as bulk materials, surfaces and interfaces with and without disorder. The approach is based on a microscopic treatment of solids and implemented using a Green function method within the density functional theory.
The efficiency of our method will be illustrated through the comparison with recent experiments on bulk materials and thin films.