Medium-sized Sin- (n=14-20) clusters: a combined study of photoelectron spectroscopy and DFT calculations

TL;DR

This study combines photoelectron spectroscopy and DFT calculations to investigate medium-sized silicon clusters (n=14-20), identifying their low-energy structures and evaluating the accuracy of various DFT functionals.

Contribution

It systematically assesses DFT functionals for silicon cluster energetics and discovers new structures for Si20- using a genetic algorithm-based global search.

Findings

HSE06 functional performs best for silicon clusters.

Most low-energy structures are assembled from tricapped trigonal prisms.

A new structure for Si20- was identified.

Abstract

Size-selected anionic silicon clusters, Sin- (n=14-20), have been investigated by photoelectron spectroscopy and density functional theory (DFT) calculations. Low-energy structures of the clusters are globally searched for by using a genetic algorithm based on DFT calculations. The electronic density of states and VDEs have been simulated by using ten DFT functionals and compared to the experimental results. We systematically evaluated the DFT functionals for the calculation of the energetics of silicon clusters. CCSD(T) single-point energies based on MP2 optimized geometries for selected isomers of Sin- are also used as benchmark for the energy sequence. The HSE06 functional with aug-cc-pVDZ basis set is found to show the best performance. Our global minimum search corroborates that most of the lowest-energy structures of Sin- (n=14-20) clusters can be derived from assembling tricapped trigonal prisms (TTP) in various ways. For most sizes previous structures are confirmed, whereas for Si20- a new structure has been found.