Fast Approach to Calculating Spectral Densities of Both Molecules and Solids Through Selected Configuration Interaction With Green's Functions
Luis Rangel DaCosta, University of California, Berkeley
In this work, we will discuss spectral density analysis of molecules and solids through many-body theory, using multireference basis sets in the framework of selected configuration interaction (sCI). As opposed to mean-field ab initio methods, such as density functional theory, which can struggle to accurately predict optoelectronic properties of chemical and materials systems in the general case, more expensive sCI techniques allow for controlled convergence of system properties to the exact full CI limit. sCI works by iteratively updating a reference wavefunction with a small set of determinants with large corrections to the wavefunction energy, and can calculate properties of ground-state and excited-state wavefunctions with similar levels of accuracy. We implemented a Green's function approach to calculating spectral densities for both isolated and coupled excitations on molecular (real-space) and solid (periodic) systems which scales up to systems with millions of determinants. Our prototype implementation relies heavily on sparse matrix routines with shared-memory parallelism, and we utilize unique algorithmic approaches for fast construction of excited state Hamiltonians using information only from the ground state, which greatly accelerates our approach on large systems. We successfully predict core and valence excitations for several molecules and will discuss spectral density results for molecular CO and the strongly correlated hydrogen chain.
Abstract Author(s): Luis Rangel DaCosta, Kevin Gasperich, Michel Caffarel, Anouar Benali