The benchmark geometries were the final geometries from the torsion scan at MP2/heavyaug-cc-pVTZ level of theory. Whereas, the benchmark relative energies were obtained using coupled-cluster with single, double, and perturbative triple excitations at the complete basis set limit, CCSD(T)/CBS. For the complete basis set calculation, Helgaker's 2-point extrapolation scheme was used as implemented in Psi4. Helgaker extrapolation scheme here includes a reference total energy from Hartree-Fock, correlation correction which includes correlation effects beyond HF with the MP2 method, and a delta correction, which gives a highly accurate correlation calculation with CCSD(T), accounting for the error in MP2.