Closed-shell interaction in the tetranuclear cluster As4 in Cu6Hg3As4S12 crystal

Density functional theory (DFT) and ELF and AIM methods were used to study closed-shell interactions between As3+ ions in the tetrahedral cluster As4 in the aktashite mineral Cu6Hg3As4S12. The vibronic interaction in [AsS3]3− molecular ions is shown to be responsible for the pyramidal structure and for the transition of As3+ lone-pair 4s2 to the mixed state 4s4p. The stability of As4 cluster may be associated with the overlap of the mixed-state wave-functions.