First-principles calculations of the effect of pressure on the iron-based superconductor LaFeAsO

Abstract

We perform first-principles calculations for an iron-based superconductor LaFeAsO in order to study its pressure effects. As the pressure increases, we find a change from monotonic to nonmonotonic shrinking manner in lattice constants and related crystalline parameters at 20 GPa and a structural transition from the orthorhombic to the tetragonal crystal with a disappearance of the antiferromagnetically ordered moment at 24 GPa in an excellent agreement with an experimental observation. Moreover, the calculations reveal that the structural transition is almost the phase transition of the second order. We further explore a very high-pressure range and find that the contraction of the distance between As and Fe plane stops above 100 GPa although the $c$-axis lattice constant continues to shrink.