Gold nanoclusters (GNCs) protected by N-heterocyclic carbenes (NHCs) and halides are promising candidates for cancer therapy. These systems feature a superatomic gold core with closed-shell electronic structure, while NHC ligands form a stabilizing shell that enhances photophysical properties[2]. Their chemical, physical, and biological behavior can be tuned through ligand modification. Molecular dynamics (MD) simulations are essential for describing their behavior in biological environments and predicting macroscopic properties such as stability and solubility, but their accuracy depends on the quality of the underlying force field.
Recent force fields for NHC–GNCs provide reliable bonded parameters compatible with AMBER, but nonbonded interactions remain less developed[2]. Atomic charges are typically derived from RESP fitting, while van der Waals parameters are adjusted to reproduce macroscopic observables, which may be insufficient for organometallic systems. Here, we introduce nonbonded parameters derived directly from electron density partitioning of NHC–GNCs. We provide Lennard-Jones parameters and atomic charges for mono- and bidentate NHC–\(\mathrm{Au}_{13}\) clusters using the theory of atom-in-molecules[3] (AIM). The resulting AIM-based parameters reproduce electrostatic, dispersion, and Pauli repulsion energies at near ab initio accuracy. Their transferability is assessed across chemical environments, and charge redistribution in the gold core and ligands is analyzed to quantify coordination effects. Validation against electrostatic potentials and energy decomposition analyses shows robust performance, with particular accuracy in describing \(\pi-\pi\) interactions between ligands.

References

[1] M. Walter, J. Akola, O. Lopez-Acevedo, P. D. Jadzinsky, G. Calero, C. J. Ackerson, R. L. Whetten, H. Gr¨onbeck and H. H¨akkinen, Proceedings of the National Academy of Sciences, 2008, 105, 9157–9162.
[2] M. F. Matus, M. Sabooni Asre Hazer, S. Malola and H. H¨akkinen, Journal of Chemical Theory and Computation, 2025, 21, 12121–12132.
[3] F. Heidar-Zadeh, P. W. Ayers, T. Verstraelen, I. Vinogradov, E. V¨ohringer-Martinez and P. Bultinck, J. Phys. Chem. A, 2018, 122, 4219–4245.