Theoretical investigation of the valence states in Au via the Au-F compounds under high pressure

In addition to the known Au³⁺ and Au⁵⁺, it has recently been shown that Au is likely to possess unusual valence states in compressed Au-F compounds. However, our simulations reveal that polymeric ground-state AuF₄ shows an unexpected 6-fold coordination rather than a 4-fold one, indicating that more complete comprehending on the anomalous Au⁴⁺ is highly required. To fully understand the nature and origin of anomalous valence states in Au, we have extensively investigated the ground-state structures of Au-F compounds at high pressures using quantum mechanical computational methods. As a consequence, we identify several previously unreported (stable) AuF₂, AuF₃ and AuF₄ structures. Our results extend the known polymorphism of AuF_n compounds and offer a fundamental understanding of the origin of unusual valence states in Au that prevail at high pressure.