  Based on precise Coulomb wave functions (CWFs), we attempt to calculate the
fusion cross sections of light nuclei in a complex spherical square-well
nuclear potential (i.e., optical potential model). Comparing with experimental
benchmark cross section data, we can calibrate optical potential parameters
associated with D+D, D+T, D+3He, p+D, p+6Li and p+7Li fusion reactions.
Surprisingly, we find that our calculated optical potential parameters are
quite different from those of many previous results (e.g., Phys. Rev. C. 61
(2000) 024610, Nucl. Phys. A 986 (2019) 98, etc.), in which approximate Coulomb
wave functions (ACWFs) with only retaining the leading terms are exploited for
the continuity conditions at the radius of nuclear potential. Furthermore, with
the obtained optical potential parameters, we compare the fusion cross sections
and astrophysical S-factors with that formulated from ACWFs approach, and also
find apparent deviations especially for the fusion reactions with resonance
peaks such as D+T and D+3He fusion reactions. We then calculate the phase
diagrams of the fusion cross sections with respect to the optical potential
parameters and demonstrate several narrow shape resonance belts. It implies
that a small deviation of ACWFs from the exact CWFs at nuclear radius might
lead to fall off the resonance regimes and therefore causes the big difference
on the optical parameters as well as the cross sections.
