Our team investigates and optimizes material functionalities for energy technologies, including next-generation solar cells, solar-fuel conversion, batteries, and ultrathin-film optoelectronics. Our research also encompasses energy-related aspects of high-temperature steelmaking processes, with particular focus on iron, iron oxides, steel, and high-κ oxides to support machine-learning simulations and experimental measurements in metallurgy. We model, compute, and analyze materials and material structures to understand fundamental materials physics, support experimental research, and explore novel material architectures. By modeling materials at the atomistic and nanoscale levels, we investigate their electronic and optical properties, thermodynamic and structural stability, and the effects of defects, particles, and alloying, with particular emphasis on interfaces between different materials. This knowledge enables us to tailor materials and interfaces to achieve optimized performance in material systems. In this project, we compute and analyze a range of unconventional alloys and their defects. Particular attention is given to copper-based solar-cell materials and non-traditional semiconductor alloys. For the development of inorganic photovoltaic devices based on ultrathin photon-absorbing films, materials must combine optimized band-gap energies with very high absorption coefficients, particularly in the low-energy part of the solar spectrum. We therefore investigate strategies for tailoring materials to produce direct-gap, multi-valley bands with suitable band-edge levels. Using such tailored materials, we demonstrate with SCAPS device simulations that sufficiently high photovoltaic efficiencies can be achieved with absorber-film thicknesses of approximately 100--500 nm. During the past year, we have also investigated the wettability of liquid metals on refractory oxides, as well as particle interactions in various fluids. The aim is to describe processes in metallurgy. We combine density-functional theory (DFT) calculations with Casimir--Lifshitz dispersion forces to analyze fundamental physical interactions. In this research direction, we model how interactions between mesoscale particles and solid surfaces are influenced by magnetic fluids or by molten steel. Our team has particular expertise in van der Waals interactions in DFT and in Casimir‒Lifshitz/Polder dispersion forces. We investigate these materials using state-of-the-art computational methods. Our scientific approaches are primarily based on the Kohn--Sham formulation within the DFT. We employ standard and meta-generalized-gradient approximations, as well as hybrid exchange-correlation functionals, the latter involve computationally intensive calculations in terms of both computational time and memory requirements. Impact of temperature is included by ab initio molecular dynamics (AIMD). The results from the calculations are integrated into mesoscale models and simulations to ultimately describe the materials' impact on the device's performance.