It must be stressed that supporters of the two different bonding models in PCMs usually work with different methodologies, which explains in great part their conflicting views. Researchers working with the metavalent bonding model have mainly adopted a phenomenological view and focused on the different properties of the materials, such as electrical and thermal conductivity, optical dielectric constant, Born effective charges, and phonon anharmonicity. Moreover, they used the QTAIM methodology to analyze the topology of the electron density and evaluate the ES and ET values . Alternatively, researchers supporting the ERMB model have paid more attention to the projected force constants between atoms, the chemical interactions between LEPs and antibonding orbitals σ* of covalent ppσ-bonds and the associated electronic band structure of the materials . These researchers have analyzed chemical interactions through the charge density, ρ, and its Laplacian, ∇ 2 ρ, at bond critical points (BCPs), the electronic density of states (DOS), the ELF, the crystal-orbital overlap population (COOP), the projected crystal-orbital Hamiltonian population (pCOHP) along the different bonds between two atoms and its integrated value, IpCOHP(2c), and COBI (including ICOBI(2c) and ICOBI(3c)). Furthermore, the supporters of the ERMB model have proposed an explanation for the linear bonding configurations present in PCMs on the basis of the valence shell electron repulsion (VSEPR) theory . They have classified the molecular units in amorphous and crystalline phases of GST depending on whether they violate or not the octet rule; the molecular units obeying the octet rule are composed by pure ordinary covalent bonds and LEPs and those violating the octet rule are composed by at least one ERMB in addition to other possible covalent bonds or LEPs .