We present an optimal 25-point finite-difference subgridding scheme for solving the 2DHelmholtz equation with perfectly matched\nlayer (PML). This scheme is second order in accuracy and pointwise consistent with the equation. Subgrids are used to discretize\nthe computational domain, including the interior domain and the PML. For the transitional node in the interior domain, the finite\ndifference equation is formulated with ghost nodes, and its weight parameters are chosen by a refined choice strategy based on\nminimizing the numerical dispersion. Numerical experiments are given to illustrate that the newly proposed schemes can produce\nhighly accurate seismic modeling results with enhanced efficiency.
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