Ab initio study of pressure–induced metallization and superconductivity in orthorhombic LiBH2 phase under ultra-high pressure

•A high–pressure orthorhombic LiBH2 phase is proposed by using CALYPSO.•oS16-LiBH2 may be an intermediate phase involved in dehydriding Pnma-LiBH4.•oS16-LiBH2 turns its semiconductor into a conducting property from 150 to 200 GPa.•oS16-LiBH2 has a potential superconductivity under ultra-high pressure.•Pressure–induced phonon softening has a great impact on the Tc of oS16-LiBH2. Hydrogen–rich materials are expected to become high–temperature superconductors after their metallization at pressures considerably lower than pure hydrogen. Combined with light elements Li and B, a high–pressure orthorhombic stable LiBH2 phase at 150 GPa is proposed by using CALYPSO and ab initio calculations. oS16-LiBH2 may be a highly plausible intermediate phase involved in dehydriding Pnma-LiBH4. Meanwhile, oS16-LiBH2 turns its semiconductor into a conducting property within the pressure range of 150 to 200 GPa and exhibits stronger conductivity along with an increasing pressure. Our electron–phonon coupling calculations reveal the softening of transverse acoustic mode B3u enhances the superconductivity of oS16-LiBH2 above 300 GPa, and its λ and Tc values increase to 1.15 and 10 K under 600 GPa, respectively. Furthermore, when the pressure exceeds 700 GPa, the B3u phonon softening makes oS16-LiBH2 dynamically unstable. Pressure–induced phonon softening may effectively improve the superconducting properties of hydrides within a certain pressure range.