  This study evaluates the precision of widely recognized quantum chemical
methodologies, CCSD(T), DLPNO-CCSD(T) and localized ph-AFQMC, for determining
the thermochemistry of main group elements. DLPNO-CCSD(T) and localized
ph-AFQMC, which offer greater scalability compared to canonical CCSD(T), have
emerged over the last decade as pivotal in producing precise benchmark chemical
data. Our investigation includes closed-shell, neutral molecules, focusing on
their heat of formation and atomization energy sourced from four specific small
molecule datasets. Firstly, we selected molecules from the G2 and G3 datasets,
noted for their reliable experimental heat of formation data. Additionally, we
incorporate molecules from the W4-11 and W4-17 sets, which provide high-level
theoretical reference values for atomization energy at 0 K. Our findings reveal
that both DLPNO-CCSD(T) and ph-AFQMC methods are capable of achieving a
root-mean-square deviation (RMSD) of less than 1 kcal/mol across the combined
dataset, aligning with the threshold for chemical accuracy. Moreover, we make
efforts to confine the maximum deviations within 2 kcal/mol, a degree of
precision that significantly broadens the applicability of these methods in
fields such as biology and materials science.
