If related information is rare in the literature, benchmark calculations are carried out to assess possible errors of various approximations employed in solving the exact electronic Schrodinger equation. Pioneering chemists have proposed several composite protocols to effectively obtain highly accurate electronic energies, such as the Gaussian-n theory, the Weizmann-n approach, the complete basis set (CBS) model, the focal point analysis (FPA), and the High accuracy Extrapolated Ab initio Thermochemistry (HEAT) protocol. In these methods, the accuracy can be systematically achieved by including various basis set extrapolation procedures, higher-order correlations, and some small corrections (core electron correlations, relativistic, spin-orbit, basis set superposition effect, diagonal Born-Oppenheimer corrections, etc.). Most were tacitly neglected in theoretical calculations. As demonstrated in the F + H2O → HF + OH reaction, the FPA and HEAT calculated barrier heights are about 2 kcal/mol lower than that predicted at the MRCI with Davidson correction, MRCI+Q/AVTZ, level. Following FPA, the geometries of stationary points were firstly determined by the all-electron (AE) UCCSD(T)-F12 method with the basis set cc-pCVTZ-F12, which takes the core-electron correlation effect into account. Then a series of single-point energy calculations are carried out to obtain the benchmark FPA or HEAT energy, namely, EFPA = E(FC-CCSDT(Q))/CBS + Δcore + Δrel + Δcore + ΔSO + ΔDBOC (1) In Eq. ( ), the complete basis set (CBS) limit is extrapolated according to results calculated at the AVXZ (X=5 and 6) basis sets. The electron correlation contribution beyond UCCSD(T) is obtained by running UCCSDT/AVTZ and UCCSDT(Q)/AVTZ calculations. The core-electron correlation effect, Δcore, is taken as the difference between AE and FC UCCSD(T)/aug-cc-pCVQZ energies. The scalar relativistic effect, Δrel, is computed by the AE Douglas-Kroll-Hess UCCSD(T)/aug-cc-pCVQZ calculation (DKH2). The spin-orbital correction, ΔSO, can be taken from available experimental measurements or can be calculated. The diagonal Born-Oppenheimer correction, ΔDBOC, determined by the HF calculation, has been demonstrated sufficiently accurate. Sub-chemical accuracy is generally expected by FPA or HEAT, or similar composite approaches. The intrinsic reaction coordinate (IRC) analysis can provide important information along the reaction coordinate. The potential energy curve along the IRC is expected to significantly affect the reaction kinetics and dynamics. Along the IRC, the reactants, products or intermediates, and transition states are connected. Accordingly, the electronic structure information is altered significantly. It is useful and efficient to test the performance of the electronic structure approach on the potential energy curve along the IRC. For instance, the reactant asymptote F( 2 Pu) + H2O(X 1 A1) has three nearly degenerate lowest-lying electronic states, while there are two nearly degenerate lowest-lying electronic states in the product asymptote HF(X 1 ∑ + ) + OH(X 2 Π). From reactants to products, at least three low-lying electronic states are therefore needed to be considered in the electronic structure calculation: the two lowest electronic states correlate adiabatically to both reactants and products and one excited state in the reactant side correlates to HF(X 1 ∑ + ) + OH(A 2 ∑ + ), namely, ground state HF and excited state OH. In addition, the situation is even more complicated near the transition state by charge transfer states. Non-adiabatic effect may occur via derivative, Renner-Teller, and spin-orbital coupling, which are useful to rationalize the non-adiabatic transitions observed in Nesbitt's experiments. Therefore, multi-reference methods, such as CASPT2 or MRCI, are suggested to provide reliable descriptions for all regions. Indeed, the tests by Deskevich, Nesbitt, and Werner showed that even the three state-averaged CASSCF (3-state-SA-CASSCF)