In Section 4.2.2, we assumed that these species are our anchors from which all other species are formed. Using the DFT energies of these species as the anchor values, it followed that the ∆ A H of CH 4 , H 2 O, H 2 , and Pt(111) in the anchor frame A are 0 because it is a null reaction. In the global thermochemical network, ∆ f H of these species are referenced to the IUPAC anchor species in their standard state. Thus, ∆ f H of the reference species have known values as listed in Table . To utilize the tabulated ∆ f H of the gas-phase species from the global network, we have to reference the DFT data to the IUPAC anchors, which we do through our chosen reference species in the atomic basis set, shown in the thermochemical cycle in Fig. . From the thermochemical cycle, it can be easily seen that ∆ f H P in the IUPAC anchor frame is the sum of the ∆ f H of the reference species and the reaction enthalpy to form the target from the references.