Comments on “Direct-Splitting-Based CN-FDTD for Modeling 2-D Material Nanostructure Problems”

The authors proposed an unconditionally stable perfectly matched layer (PML) based on the Crank-Nicolson direct-splitting (CNDS) method to analyze nanostructure problems in
[1]
. However, there are concerns regarding the correctness and validity of the mathematical derivations and numerical results, shown in the original manuscript. These concerns can be summarized into the following three aspects.