The Structure of Adamantane Clusters: Atomistic vs. Coarse-Grained Predictions From Global Optimization

Abstract

Candidate structures for the global minima of adamantane clusters, (C 10 H 16 ) N , are presented. Based on a rigid model for individual molecules with atom-atom pairwise interactions that include Lennard-Jones and Coulomb contributions, low-energy structures were obtained up to N = 42 using the basin-hopping method. The results indicate that adamantane clusters initially grow accordingly with an icosahedral packing scheme, followed above N = 14 by a structural transition toward face-centered cubic structures. The special stabilities obtained at N = 13, 19, and 38 are consistent with these two structural families, and agree with recent mass spectrometry measurements on cationic adamantane clusters. Coarse-graining the intermolecular potential by averaging over all possible orientations only partially confirm the all-atom results, the magic numbers at 13 and 38 being preserved. However, the details near the structural transition are not captured well, because despite their high symmetry the adamantane molecules are still rather anisotropic.

Effects of oxidative adsorbates and cluster formation on the electronic structure of nanodiamonds

“…For the mixed diamondoid aggregates, these orbitals are partly localized at one particular molecule and partly delocalized over several molecules. This confutes the previous assumption that no electron delocalization occurs between the different molecules of a cluster 33.…”

“…48 Note that the use of augmented basis sets was not feasible for the larger structures in the first part of the study. It is known that alone for the adamantane dimer more than 20 local minimum structures exist within 2 kJ/mol of the putative global minimum, 33 however, slight changes in the structures' geometries did not have a significant impact on the properties presented herein. The diamondoids' HOMO-LUMO gap (HLG) values were corrected according to the zero-point energy gap renormalizations (ZPR) as calculated by Han et al 52 For the dimers and higher adamantane clusters, no ZPR corrections have been calculated explicitly, but we use the respective monomer corrections as a proxy instead.…”

“…Furthermore, it is known from experiments that NDs tend to form clusters and self-assembled networks in solution. 31,32 Theoretical work has been conducted on the aggregation behavior 32 and stability 33 of those clusters as well as on the electronic properties of single isolated NDs, 34 but the effects of cluster formation on the NDs' electronic properties are so far unexplored.…”

Predicting dipole orientations in spontelectric methyl formate

“…The parameter R and ε depend on the types of atom that are involved in the interaction. For dissimilar types, the Lorentz-Berthelot combination rule [32] is used and contributions of adjacent atoms are not accounted for according to the 1-4 exclusion scheme [30]. Furthermore, the intramolecular bonded contribution is given by the addition of bond, angle and dihedral terms: Here, c b , c a , c d denote spring constants, R b is an equilibrium distance, θ a an equilibrium angle, n the multiplicity and δ an equilibrium phase.…”