In nonpolar, small-sized colloidal NC systems, ligand tail chains play a critical role in determining interparticle interactions and assembly dynamics. Our focus was on engineering the ligand tails, derived from octadecane (OD, Figure ), by incorporating various molecular fragments and functional groups-such as carbon-carbon double bonds (DB), branched chains (BC), benzene rings (BR), and naphthalene rings (NR)-at different positions along the chain (proximal (p, i.e., near the head group), middle (m), distal (d), proximal-middle (pm), and middle-distal (md)), while maintaining a constant total number of carbon atoms (18) in the ligand tails (Figure ). Ligands were named according to the position and type of modification; for instance, a ligand with a benzene ring at the proximal position is labeled as pBR. Additionally, we examined ligands with subtle positional adjustments and combinations of two different fragments (Figure ). For positional adjustments, the new location is indicated by a number representing the number of carbon atoms shifted toward the head group (e.g., d1BR in Figure ). For ligands with two different fragments, a hyphen connects the two groups (e.g., mDB-dBR in Figure ). We initially placed a bare PbSe core into a solution containing 800 ligand and 30000 solvent molecules, allowing the ligands to adsorb freely onto the PbSe NC surface (Figure , Methods). Figure shows the adsorption kinetics of OD ligands on PbSe over time, while the adsorption kinetics for other ligands are shown in Fig. . After 200 ns of simulation, ligand adsorption reached near saturation (Figure and Fig. ). Figure shows the final configurations of DB, BC, BR, and NR ligands at different positions (p, pm, m, md, d). Our force field was parametrized based on DFT-calculated binding energies for oleic acid on the {100} surface (0.16 eV) and oleate on the {111} surface (0.52 eV). We observed that all ligand types preferentially adsorbed onto the {111} surfaces rather than the {100} surfaces. If it is a carboxyl or amino group, OD corresponds to it is a carboxyl or amino group, and mDB corresponds to oleic acid or oleylamine, which are common ligands used in the synthesis, storage, and self-assembly of colloidal NCs. Therefore, PbSe NCs, particularly in IV-VI groups, may expose {100} facets, consistent with experimental observations of oriented attachment and crystal growth on this facet. Figure shows the maximum number of adsorbed ligands (n max ) for each type of ligand modification. The value of n max ranged from 350 to 450 per NC, corresponding to a ligand density of 4.5-5.7 ligands/nm 2 . This density range is slightly higher than the TGA-measured ligand densities for oleic acid and thiols on NCs (3-4.5 ligands/nm 2 ). In experiments, multiple alcohol washings are often employed to remove weakly bound ligands, 50 so the measured densities are expected to be lower than the saturated adsorption density. Our simulations provide a reasonable description of ligand passivation on colloidal NCs. As shown in Figure , ligands modified at the distal positions exhibited higher adsorption numbers than those modified at the proximal positions. This trend can be attributed to the steric hindrance introduced by the molecular fragments, particularly for BC, BR, and NR.