Efficient method for twist-averaged coupled cluster calculation of gap energy: Bulk study of stannic oxide

We study the gap energy of the semiconducting oxide SnO2 through ab initio calculations including both density functional theory (DFT) and coupled cluster methods. The effectiveness of twist averaging in reducing finite-size errors is evaluated across different functionals. We report an overestimation of gap energy when applying finite-size scaling to reach the thermodynamic limit in equation-of-motion (EOM) CCSD calculations. To mitigate one-body and many-body errors, we integrate twist averaging with a post-processing correction mechanism that compares finite-size and infinite-size DFT calculations using hybrid functionals. While inspired by the Kwee, Zhang, and Krakauer approach, our method is specifically tailored to hybrid functionals for a more accurate treatment of exchange-correlation effects. Our approach ensures that the many-body interactions are accurately captured in the estimated gap for an infinite system. We introduce unique single twist angles that provide cost-effective and accurate energies compared to to full twist averaging in EOM-CCSD calculations. Applying this approach to SnO2, we calculate a fundamental gap of 3.46 eV, which closely matches the 3.59 eV gap obtained from two-photon spectroscopy experiments, demonstrating the accuracy of this method.