In the Letter of Xiang et al., a novel, metastable cubic silicon phase Si₂₀-T was theoretically predicted by the modified particle swarm optimization method CALYPSO. The optical absorption of this phase was computed and compared to that of diamond silicon. Si₂₀-T exhibits a quasidirect gap of 1.55 eV and has a stronger absorption in the visible compared to diamond silicon, which makes it a candidate as a solar energy absorber. However, we have strong reasons to believe that this phase cannot be experimentally synthesized via strong compression or decompression or through molecular encapsulation as proposed by the authors.