  Evolutionary crystal structure prediction searches have been employed to
explore the ternary Li-F-H system at 300 GPa. Metastable phases were uncovered
within the static lattice approximation, with LiF$_3$H$_2$, LiF$_2$H,
Li$_3$F$_4$H, LiF$_4$H$_4$, Li$_2$F$_3$H and LiF$_3$H lying within 50 meV/atom
of the 0 K convex hull. All of these phases contain H$_n$F$_{n+1}^-$ ($n$ = 1;
2) anions, and Li$^+$ cations. Other structural motifs such as LiF slabs,
H$_3^+$ molecules, and F$^{\delta -}$ ions are present in some of the low
enthalpy Li-F-H structures. The bonding within the H$_n$F$_{n+1}^-$ molecules,
which may be bent or linear, symmetric or asymmetric, is analyzed. The five
phases closest to the hull are insulators, while LiF$_3$H is metallic and
predicted to have a vanishingly small superconducting critical temperature.
This study lays the foundation for future investigations of the role of
temperature and anharmonicity on the stability and properties of compounds and
alloys in the Li-F-H ternary system.
