Atgeirr worked on the OPM/opm-common, OPM/opm-simulators, and OPM/opm-tests repositories, focusing on reliability, performance, and maintainability in reservoir simulation software. He refactored error handling and message formatting in C++ to standardize diagnostics and streamline troubleshooting, while optimizing Brine_CO2 calculations by reusing computational terms for efficiency. In OPM/opm-simulators, he improved error reporting and updated documentation to enhance user support and onboarding. He also replaced mutex-based grid processing with OpenMP parallelization, reducing synchronization overhead. Additionally, Atgeirr expanded scenario coverage in OPM/opm-tests by introducing a new two-phase gas-water simulation deck, demonstrating depth in numerical modeling and scientific computing.