  The spin-crossover in organometallic molecules constitutes one of the most
promising routes towards the realization of molecular spintronic devices. In
this article, we explore the hybridization-induced spin-crossover in
metal-organic complexes. We propose a minimal many-body model that captures the
essence of the spin-state switching in a generic parameter space, thus
providing insight into the underlying physics. Combining the model with density
functional theory (DFT), we then study the spin-crossover in isomeric
structures of Ni-porphyrin (Ni-TPP). We show that metal-ligand charge transfer
plays a crucial role in the determination of the spin-state in Ni-TPP. Finally,
we propose a spin-crossover mechanism based on mechanical strain, which does
not require a switch between isomeric structures.
