e⁺(PsH)₂: A three-positron molecule with a positronic chemical bond

Two new positronic molecules have been recently discovered: e⁺H^- ₂ [Charry et al., Angew. Chem., Int. Ed. 57, 8859 (2018)] and (PsH)₂ [D. Bressanini, J. Chem. Phys. 155, 054306 (2021)]. These molecules seem to be stabilized by a new type of bond, the positronic bond, where one or two positrons are directly responsible for the bonding of two otherwise repelling negative ions. We show that an additional positron can attach to (PsH)₂ to form a locally stable species with three positrons whose potential energy curve shows an equilibrium structure at about 8 bohr and a binding energy of 11.5(5) mhartree with respect to the dissociation into PsH + e⁺PsH. This molecule, tentatively called e⁺(PsH)₂, is the first system with three positrons discovered.