Geometric structure, electronic structure and optical absorption properties of one-dimensional thiolate-protected gold clusters containing a quasi-face-centered-cubic (quasi-fcc) Au-core: a density-functional theoretical study

Based on the recently reported atomic structures of thiolate-protected Au 28 (SR) 20 , Au 36 (SR) 24 , Au 44 (SR) 28 , and Au 52 (SR) 32 clusters, a family of homogeneous, linear, thiolate-protected gold superstructures containing novel quasi-face-centered-cubic (quasi-fcc) Au-cores is theoretically envisioned, denoted as the Au 20+8 N (SR) 16+4 N cluster. By means of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, a unified view of the geometric structure, electronic structure, magic stable size and size-dependent NIR absorption properties of Au 20+8 N (SR) 16+4 N clusters is provided. We find that the Au 20+8 N (SR) 16+4 N clusters demonstrate oscillating transformation energies dependent on N . The odd- N clusters show more favorable (negative) reaction energies than the even- N clusters. The magic stability of recently reported Au 28 (SR) 20 , Au 36 (SR) 24 , Au 44 (SR) 28 , Au 52 (SR) 32 and Au 76 (SR) 44 clusters can be addressed from the relative reaction energies and geometric distortion of Au-cores. A novel 4 N + 4 magic electron-number is suggested for the Au 20+8 N (SR) 16+4 N cluster. Using the polyhedral skeletal electron pair theory (PSEPT) and the extended Hückel molecular orbital (EHMO) calculations, we suggest that the magic 4 N + 4 electron number is correlated with the quasi-fcc Au-cores, which can be viewed as double helical tetrahedron-Au 4 chains. The size-dependent optical absorption properties of Au 20+8 N (SR) 16+4 N clusters are revealed based on TD-DFT calculations. We propose that these clusters are potential candidates for the experimental synthesis of atomically precise one-dimensional ligand protected gold superstructures with tunable NIR absorption properties. A family of homogeneous linear thiolate-protected gold superstructures Au 20+8 N (SR) 16+4 N containing novel quasi-face-centered-cubic (quasi-fcc) Au-cores is theoretically envisioned.