First, we evaluate the accuracy and convergence of our DLPNO-CCSDT algorithm on a benzene molecule (cc-pVDZ basis, 114 basis functions), as well as a linear fulminic acid (HCNO) structure (cc-pVTZ basis, 104 basis functions) in Figures and, comparing it to the results of the preceding DLPNO-CCSD(T) computation. The geometry for the benzene molecule is provided in the supplementary material, while the linear HCNO geometry is derived from the work of Allen et al., optimized at the AE-CCSDTQ(P)/CBS + MVD1 level of theory. The canonical CCSD(T) and CCSDT energies for benzene are computed through the MRCC software, while the reference energies for HCNO are derived from the work of Allen et al. For HCNO, a cc-pV5Z-RI basis set is used for the RI domain in our DLPNO computations to control for RI error. In Figures and, the ratio of the DLPNO-CCSDT correlation energy with respect to the canonical CCSDT energy is computed as a function of the TNO tolerances of the strong and weak triplets (see section IIC subsection 5), and then compared to the percent recovery of the canonical CCSD(T) energy in the preceding DLPNO-CCSD(T) computation. Per Riplinger et al., for chemical accuracy, a good target is the recovery of at least 99.9% correlation energy. However, applications of CCSDT require an order of magnitude higher accuracy to reach kJ mol -1 accuracy. Therefore, a good standard for applications of DLPNO-CCSDT is to recover no less than 99.99% and no more than 100.01% of the canonical CCSDT correlation energy. The dotted red lines in Figures and represent our desired accuracy. In both cases, the target accuracy of CCSDT is achieved at a strong pair/weak pair TNO tolerance of 10 -8 /10 -7 , which happen to be the default settings for DLPNO-CCSD(T). Therefore, unless otherwise stated, all DLPNO-CCSDT computations reported in subsequent sections will be computed using these parameters. It is interesting to note the difference in convergence behavior be- T STRONG SCALE , and T WEAK SCALE . The results show strong agreement between the CCSDT and DLPNO-CCSDT computed reaction enthalpies and barrier heights, with the highest error being 0.12 kcal mol -1 (around 0.5 kJ mol -1 ). It is an especially encouraging observation that the magnitude of the error between DLPNO-CCSDT and canonical CCSDT is invariant to the magnitude of δ CCSD(T) CCSDT . We do, however, strongly caution the use of taking the difference between DLPNO-CCSDT and DLPNO-CCSD(T) energies to estimate δ CCSD(T) CCSDT . Though the errors between δ