To determine whether it is necessary to use spin-orbit-coupling (SOC) to identify low-energy structures for heavy-metal elements, we performed additional PBE + SOC calculations on the lowest energy clusters of 11 different heavy-metal elements (Au, Bi, Hf, Hg, Ir, Os, Pb, Pt, Re, Ta, and Tl) with sizes ranging from 3 to 55 atoms. Additionally, we choose the six (where available) lowest energy isomers for small (size 10), medium (size 30), and large (size 55) clusters to study the effect of SOC on relative ordering. The PBE+SOC calculated energies linearly correlated with PBE computed energies (Figure ). We also developed a cheap proxy to evaluate PBE+SOC computed energies from PBE computed energies for these 11 different elements using linear regression. The conversion factors (slope and intercept) for converting PBE+SOC energies from PBE energies for these elements are provided in Figure . We also found that the use of SOC has little effect on the energetic rankings of isomers (Figure , Figure , and Figure ). For these reasons, and to maintain consistency in the database, we have not included the effects of SOC in the calculated energies in the QCD. For three small clusters (with compositions Pb10, Tl10 and Hf10), the PBE + SOC calculations relaxed to clusters that were structurally dissimilar to the relaxed PBE structures (as determined by similarity scores greater than 0.3). Because the energies for the two methods were not calculated for the same structure, these clusters are excluded from the comparisons in Figure , Figure and Figure .