An eighth-order Runge-Kutta(R-K)recurrence formula is constructed for differential equations.The formula i8 used tu simulate formation and movement of polarons in a one-dimensional poly-phenylenevinylene(PPV)molecular chain.The PPV chain composed of N carbons is described by an extended tight binding model.For N=160.the equations are solved by eighth.order R.K method.Stable polaron configuration and moving picture are obtained.Under electric field E=1×10⁵V×cm^-1.a poiaron moved along PPV chain at a velocity of 0.263 5Å·fs^-1.It indicates that the eighth-order R-K formula is applicable to carrier movement in organic molecules.

For a magnetic tunneling junction with ferromagnetic metal/magnetic potential barrier layer/ferromagnetic metal structure, tunneling conductance, spin polarization and tunneling magneto resistance rate under zero bias voltage are calculated in a quasi-free electron model. The impact of potential barrier, molecular field strength and molecular field orientation, etc. on tunneling of electrons is analyzed. It exhibits useful instructions for the design of spin electronic devices.