  With the extension of the spectral exploitation of optical fibers beyond the
C-band, accurate modeling and simulation of nonlinear interference (NLI)
generation is of the utmost performance. Models and numerical simulation tools
rely on the widely used Manakov equation (ME): however, this approach when
considering also the effect of polarization mode dispersion (PMD) is formally
valid only over a narrow optical bandwidth. In order to analyze the range of
validity of the ME and its applicability to future wide-band systems, we
present numerical simulations, showing the interplay between NLI generation and
PMD over long dispersion-uncompensated optical links, using coherent
polarization division multiplexing (PDM) quadrature amplitude modulation (QAM)
formats. Using a Monte-Carlo analysis of different PMD realizations based on
the coupled nonlinear Schr\"{o}dinger equations, we show that PMD has a
negligible effect on NLI generation, independently from the total system
bandwidth. Based on this, we give strong numerical evidence that the ME can be
safely used to estimate NLI generation well beyond its bandwidth of validity
that is limited to the PMD coherence bandwidth.
