Spectral Density Calculations for Solids with Selected Configuration Interaction

In this presentation, we will discuss spectral density analysis of molecules and solids through many-body theory, using multireference wavefunctions in the framework of selected configuration interaction (sCI). This method allows controlled convergence to the full CI limit within a given basis set at a fraction of the cost by iteratively updating a reference wavefunction with a small set of determinants with large contributions to the wavefunction energy. sCI can calculate properties of ground-state and excited-state wavefunctions with similar levels of accuracy, making it a unique ab initio method. We implemented a Green's function approach to calculating spectral densities, for which we will discuss relevant computational pragmatic strategies and convergence behaviors. We successfully predict core and valence excitations for several molecules and will discuss spectral density results for the strongly correlated hydrogen chain and periodic silicon.