  Metal-insulator transition underlies many remarkable and technologically
important phenomena in VO2. Even though its monoclinic structure had before
been the reserve of the insulating state, recent experiments have observed an
unexpected monoclinic metallic state. Here we use a modified approach combining
first-principles calculations with orbital-biased potentials to reproduce the
correct stability ordering and electronic structure of different phases of VO2.
We identify a ferromagnetic monoclinic metal that is likely to be the
experimentally observed mysterious metastable state. Furthermore, our
calculations show that an isostructural insulator-metal electronic transition
is followed by the lattice distortion from the monoclinic structure to the
rutile structure. These results not only explain the experimental observations
of the monoclinic metallic state and the decoupled structural and electronic
transitions of VO2, but also provide a understanding for the metal-insulator
transition in other strongly correlated d electron systems.
