Prediction of a new layered phase of nitrogen from first-principles simulations

A new phase of nonmolecular nitrogen has been suggested by first-principles density functional theory simulations at high pressures. The phase has zigzag chains similar to the BP, A7 and LB phases, but the zigzag chains in the PP phase are connected by two atoms with double bonds with Pmna symmetry, which we designated as the PP phase. Properties of PP are presented in comparison with other polymeric phases of nitrogen discussed previously. The calculated enthalpy versus pressure reveals a similarity between the PP and CH phases. The equation of state of nitrogen in the PP, CG and e phases shows that an e transition to the PP phase happens at 90 GPa. The band structure and bulk modulus of PP phase are also calculated.