Given the promise of U parameters calibrated on SBU models to improve the energetics of full periodic MOFs, we investigated whether we could increase the fidelity with which we model the SBU. CCSD(T) is widely regarded as the gold standard in quantum chemistry, and thus we selected it as our reference method for SBU calculations obtained at a higher level of theory. We confirmed the reliability of CCSD(T) calculations using the T1 diagnostic, which estimates the multireference character through the single-excitation amplitude vector from CCSD calculations. Apart from one exception, all systems of interest were shown to have a T1 value below 0.02 (Supporting Information Table ). The cutoff value of 0.02 is generally accepted as indicating that static correlation errors are manageable for single-reference methods. The one system exhibiting a high T1 value is Co2OH2-BBTA with an O2 adsorbate, which will be discussed in detail below. Nevertheless, the ultimate test for theoretical calculations should be experimental reference data. As a more stringent test, we investigated the effectiveness of the U parameter fitted to SBU CCSD(T) calculation results, U CCSD(T) , in predicting the experimental heat of adsorption for the periodic MOF. This corresponds to the same approach as USBU fitting where each adsorbate and MOF gets its own U parameter but in this case the tuning is carried out to match CCSD(T) results. For systems where experimental heat of adsorption data was available, we calculated the adsorption energy for N2, CO2, and O2 using PBE and PBE+U CCSD(T)