  A previously unknown thermodynamically stable high-pressure phase of
BeF$_{2}$ has been predicted using the evolutionary algorithm USPEX. This phase
occurs in the pressure range 18-27 GPa. Its structure has $C2/c$ space group
symmetry and contains 18 atoms in the primitive unit cell. Given the analogy
between BeF$_{2}$ and SiO$_{2}$, silica phases have been investigated as well,
but the new phase has not been observed to be thermodynamically stable for this
system. However, it is found to be metastable and to have comparable energy to
the known metastable phases of SiO$_{2}$, suggesting a possibility of its
synthesis.
