Efficient Method for Twist-Averaged Coupled Cluster Calculation of Gap Energy: Bulk Study of Stannic Oxide

We study gap energy of the semiconducting oxide SnO2 through ab-initio calculations. DFT and coupled cluster calculations are presented and discussed. In this work, we emphasize that GGA+U does not improve the physics of the semicore d electrons in SnO2. We report an overestimation in the gap energy by finite-size scaling at the thermodynamic limit through equation-of-motion (EOM) CCSD calculations. To address one-body and many-body errors, we report a combination of the Kwee-Zhang-Krakauer (KZK) approach with twist averaging to explain twist averaged EOM-CCSD gap energy. In this approach, the correction to the gap energy originates from the difference between mean-field and many-body approximations and at the end the difference is added to the mean-filed gap of an infinite system to estimate the many-body gap in the thermodynamic limit. The efficiency of the twist averaging in reducing the finite-size errors is tested through different functionals.