  We propose a self-consistent model which utilizes the polarization vector to
theoretically describe the evolution of spin polarization of relativistic
electrons in an intense electromagnetic field. The variation of radiative
polarization due to instantaneous no photon emission is introduced into our
model, which extends the applicability of the polarization vector model derived
from the nonlinear Compton scattering under local constant crossed-field
approximation to the complex electromagnetic environment in laser plasma
interaction. According to this model, we develop a Monte Carlo method to
simulate the electron spin under the influence of radiation and precession
simultaneously. Our model is consistent with the quantum physical picture that
spin can only be described by a probability distribution before measurement,
and it contains the entire information on the spin. The correctness of our
model is confirmed by the successful reproduction of the Sokolov-Ternov effect
and the comparison of the simulation results with other models in the
literature. The results show the superiority in accuracy, applicability, and
computational efficiency of our model, and we believe that our model is a
better choice to deal with the electron spin in particle-in-cell simulation for
laser plasma interaction.
