Computing Ionization Potentials of Heavy Atoms using Selected Configuration Interaction Methods

The design and functionality of future plasma fusion power plants will depend on access to accurate atomic data relevant to the material chosen as the plasma-facing component in a fusion device. A common choice for this purpose is tungsten due to its high melting point, but its ionization potentials are crucial values for accounting energy losses from inevitable leakage into the core plasma. The energy states of heavy atoms with many electrons such as tungsten are difficult to calculate with high accuracy, so there exist gaps and large uncertainties in the available data. We aim to address these shortcomings by using the Semistochastic Heat-Bath Configuration Interaction (SHCI) method, which is an approximation of the full configuration interaction capable of calculating accurate energies for atoms and small molecules. Adding well-motivated approximations to SHCI, including orbital optimization and effective core potentials, we demonstrate good agreement between our calculated ionization energies and the best available experimental and theoretical values for chromium and molybdenum. The accuracy achieved in calculating these ionization potentials demonstrates that our SHCI workflow can produce better data for tungsten and other heavy atoms to aid new applications.