  A fast explicit operator splitting (FEOS) method for the molecular beam
epitaxy model has been presented in [Cheng, et al., Fast and stable explicit
operator splitting methods for phase-field models, J. Comput. Phys.,
submitted]. The original problem is split into linear and nonlinear
subproblems. For the linear part, the pseudo-spectral method is adopted; for
the nonlinear part, a 33-point difference scheme is constructed. Here, we give
a compact center-difference scheme involving fewer points for the nonlinear
subproblem. Besides, we analyze the convergence rate of the algorithm. The
global error order $\mathcal{O}(\tau^2+h^4)$ in discrete $L^2$-norm is proved
theoretically and verified numerically. Some numerical experiments show the
robustness of the algorithm for small coefficients of the fourth-order term for
the one-dimensional case. Besides, coarsening dynamics are simulated in large
domains and the $1/3$ power laws are observed for the two-dimensional case.
