Atomistic Modeling of Quantum Dots at Experimentally Relevant Scales Using Charge Equilibration

Quantum dots (QDs) have been successfully employed within a vast array of fundamental and applied studies spanning all subdisciplines of chemistry. However, ab initio models of QD behavior are inherently limited by computational cost due to the large number of atoms within QDs of experimentally relevant size. This work builds upon the method of charge equilibration (qEQ) to account for system interactions unique to QDs (QD-qEQ) and demonstrates accuracy through calculated per-QD energies and dipole moments that agree generally with ab initio calculations and experimental observation, respectively. By forgoing electronic structure information, QD-qEQ exhibits a distinct advantage in its exceptionally low computational cost, which affords consideration of over 35,000 unique spherical wurtzite CdSe structures with radii ≤12.5 Å. A comparison of QD-qEQ calculations with experimental data relating to the phenomenon of CdSe magic size crystals (MSCs) affords statistical and structural insight into why MSCs are observed. Consideration of structures ≤12.5 Å reveals QD sizes corresponding with local minima in QD energy, correlating closely with experimentally observed MSCs. The physical origin of observed energy minima is assigned to QD structures with surfaces exhibiting large fractions of highly coordinated atoms, a physical trait postulated to yield fewer reaction sites for stepwise growth, resulting in MSC stability. The low computational cost along with the per-atom and per-structure electrostatic data afforded by QD-qEQ makes this method an enticing approach to address dynamic QD behavior and enables potential applications within a broad range of fields concomitant to those in which QD inclusion has already proven useful.