  The nature of the newly proposed two-positron bond in (PsH)2, which is
composed of two protons, four electrons and two positrons, is considered in
this contribution. The study is done at the multi-component-Hartree-Fock
(MC-HF) and the Diffusion Monte Carlo (DMC) levels of theory by comparing ab
initio data, analyzing the spatial structure of the DMC wavefunction, and
applying the multi-component quantum theory of atoms in molecules and the
two-component interacting quantum atoms energy partitioning schemes to the
MC-HF wavefunction. The analysis demonstrates that (PsH)2 to a good
approximation may be conceived of two slightly perturbed PsH atoms, bonded
through a two-positron bond. In contrast to the usual two-electron bonds, the
positron exchange phenomenon is quite marginal in the considered two-positron
bond. The dominant stabilizing mechanism of bonding is a novel type of
classical electrostatic interaction between the positrons, which are mainly
localized between nuclei, and the surrounding electrons. To emphasize its
uniqueness, this mechanism of bonding is proposed to be called gluonic which
has also been previously identified as the main deriving mechanism behind
formation of the one-positron bond in [H-, e+, H-]. We conclude that the
studied two-positron bond should not be classified as a covalent bond and it
must be seen as a brand-new type of bond, foreign to the electronic bonding
modes discovered so far in the purely electronic systems.
