A subtle change in the electronic structure of thiolate-protected noble metal nanoparticles can result in distinctive energy relaxation dynamics. Corresponding investigations on different sizes and structures of thiolate-protected gold nanoclusters reveal their physical and chemical properties for further development of catalytic applications. In this work, we performed nonradiative relaxation dynamics simulations of the Au38(SH)24 nanocluster to describe electron-vibrational energy exchange. The core and higher excited states involving semiring motifs lying in the energy range of 0.00-2.01 eV are investigated using time-dependent density functional theory (TDDFT). The surface hopping method with decoherence correction combined with real-time TDDFT is used to assess the quantum dynamics. The Au23 core relaxations are found to occur in the range of 2.0-8.2 ps. The higher excited states that consist of core-semiring mixed or semiring states give ultrafast decay time constants in the range of 0.6-4.9 ps. Our calculations predict that the slowest individual state decay of S11 or the slowest combined S11-S12, S1-S2-S6-S7 and S4-S5-S9-S10 decay involves intracore relaxations. The analysis of the phonon spectral densities and the ground state vibrational frequencies suggests that the low frequency (25 cm-1) coherent phonon emission reported experimentally could be the bending of the bi-icosahedral Au23 core or the "fan blade twisting" mode of two icosahedral units.
Bibliographical noteFunding Information:
This material is based on work supported by Department of Energy under grants DE-SC0012273 to C.M.A. and DESC0014429 to O.V.P. The computing for this project was performed on the Beocat Research Cluster at Kansas State University, which is funded in part by NSF grants CHE-1726332, CNS-1006860, EPS-1006860, and EPS-0919443. Beocat Application Scientist Dr. Dave Turner provided valuable technical expertise. The authors are grateful to Prof. Alexey V. Akimov for his support and valuable discussions on PYXAID.
© 2018 American Chemical Society.