Energy Landscape analysis of metal-insulator transitions: theory and application to Ca$_2$RuO$_4$, RNiO$_3# and their heterostructures

We present a general methodology that enables the disentanglement of the electronic and lattice contributions to the metal-insulator transition by building an energy landscape from numerical solutions of the equation of state. The methodology works with any electronic structure method that provides electronic expectation values at given atomic positions. Applying the theory to rare-earth perovskite nickelates (RNiO3) and Ruddlesden-Popper calcium ruthenates (Ca2RuO4) in bulk, heterostructure and epitaxially strained thin film forms using equation of state results from density functional plus dynamical mean field calculations we show that the electron-lattice coupling is an essential driver of the transition from the metallic to the insulating state in these materials. The methodology is used to unravel strain effects in heterostructures and interpret pump-probe experiments.