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 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 at 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, comparing finite-size and infinite-size DFT calculations using hybrid functionals. While inspired by the Kwee, Zhang, and Krakauer (KZK) approach, our method is tailored to hybrid functionals for a more accurate treatment of exchange-correlation effects. Our approach ensures that the many-body interactions are accurately reflected in the estimated gap for an infinite system. We introduce unique single twist angles that yield cost- effective and accurate energies, in comparison to full twist averaging in the EOM-CCSD calculations. Applying this approach to SnO2, we calculate a fundamental gap of 3.46 eV, closely matching the 3.59 eV gap obtained from two-photon spectroscopy experiments, thereby demonstrating the accuracy of this method.