Role of octahedral distortions in the metal-insulator transition compound Ca₂MoO₄

Structural distortions play an important role in mediating materials phenomena, such as the metal-insulator transition (MIT). Having proposed Ca₂MoO₄ as a MIT for its structural and electronic similarity to the Ruddlesden-Popper perovskite (RP) Ca₂RuO₄, a known MIT, we performed density functional theory simulations to predict Ca₂MoO₄ as dynamically stable in the same Pbca space group as Ca₂RuO₄. In contrast to metallic Sr₂MoO₄ (I4/mmm symmetry), Ca₂MoO₄ exhibits a distorted ground state structure with octahedral rotations and cooperative Jahn-Teller distortions. We further find that electron correlation cooperatives with these structural distortions to open a band gap. We examine how coupled distortions describing the symmetry breaking from the high to low symmetry structures modulate the bandgap and contribute to the MIT. Last, we examine the effects of electron correlation and magnetism on the phase transition.