  In order to clarify phase relation of Zn2SiO4 system, first-principles DFT
calculations of 11 phases were conducted. We confirmed that phases III and IV
are retrograde phases. Instead, Na2CrO4- and Ag2CrO4-structured phases are most
likely candidate structures for high-pressure phases of III and IV,
respectively. A transition of phase II to spinel found during optimization was
discussed in relation to similar transition known for nitrides.
