Effect of spin crossovers on the Mott-Hubbard transition at high pressures.

The effect of spin crossovers in d n terms on the effective Hubbard parameter ( U eff) determining the gap between the lower and upper Hubbard bands is analyzed using a many-electron approach to describe the electron structure of Mott insulators. A new mechanism of the insulator-metal transition is established for d 5 ions, which is related to a decrease in U eff caused by spin crossover. For other ions, the U eff value is either independent of pressure ( d 2, d 4, d 7) or it exhibits nonmonotonic growth ( d 3, d 6, d 8). [ABSTRACT FROM AUTHOR]