Gold-Standard Chemical Database 138 (GSCDB138): A diverse set of accurate energy differences for assessing and developing density functionals

Abstract: We present GSCDB138, a rigorously curated benchmark library of 138 data sets (8383 entries) covering main-group and transition-metal reaction energies and barrier heights, non-covalent interactions, dipole moments, polarizabilities, electric-field response energies, and vibrational frequencies. Legacy data from GMTKN55 and MGCDB84 have been updated to today's best reference values; redundant, spincontaminated, or low-quality points were removed, and many new, property-focused sets were added. Testing 29 popular density-functional approximations shows the expected Jacob's-ladder hierarchy overall, yet reveals interesting exceptions: r2SCAN-D4 (meta-GGA) rivals hybrids for frequencies, and electric-field errors correlate poorly with ground-state energetics. {\omega}B97M-V and {\omega}B97X-V are the most balanced hybrid meta-GGA and hybrid GGA, respectively; B97M-V and revPBE-D4 lead the metaGGA and GGA classes. Double hybrids lower mean errors by about 25 % versus the best hybrids but demand careful frozen-core, basis-set, and multi-reference treatment. GSCDB138 offers a comprehensive, openly documented platform for stringent DFA validation and for training the next generation of non-empirical and machine-learned functionals.