Compressional behavior of MgCr 2 O 4 spinel from first-principles simulation

The compressional behavior of the MgCr2O4 spinel has been investigated with the CASTEP code using density functional theory and planewave pseudopotential technique. We treated the exchange-correlation interaction by both the local density approximation (LDA) and generalized gradient approximation (GGA) with the Perdew-Burker-Ernzerhof functional. Our simulation was conducted for the pressure range of 0–19 GPa. We obtained the isothermal bulk modulus (K T ) of the MgCr2O4 spinel as 181.46(48) GPa (GGA; low boundary) or 216.1(11) GPa (LDA; high boundary), with its first derivative (K' T ) as 4.41(6) or 4.5(1), respectively. The oxygen parameter u is not constant but negatively correlated with P, and decreases by about 0.5–0.6% for the investigated P range. The component polyhedra have different compressibilities, increasing in the order of (O4)1tetrahedron is much more compressible than the Cr-O bond in the CrO6 octahedron.