Optical Absorption Spectra Calculated from a First-Principles Wave Function Theory for Solids: Transcorrelated Method Combined with Configuration Interaction Singles

We present a new ab initio method for excited-state calculations based on wave function theory: transcorrelated (TC) method combined with configuration interaction singles (CIS). Conventional CIS with the HartreeFock wave function, while a popular method for excited-state calculations of molecular systems, cannot describe electron correlation effects, such as the screening effect in solids, resulting in inaccurate results such as overestimation of the band gap and exciton binding energy. Here, we adopt the TC method, which takes electron correlations into account through a similarity transformation of the Hamiltonian using the Jastrow factor, and combine it with the CIS approximation. We calculate the optical absorption spectra of solid LiF and GaAs as a test, and verify that the present method reproduces the spectra more accurately than the conventional HF-CIS. The excitonic effect is well described with our method.