  Due to the rapid longitudinal expansion of the quark-gluon plasma created in
heavy-ion collisions, large local-rest-frame momentum-space anisotropies are
generated during the system's evolution. These momentum-space anisotropies
complicate the modeling of heavy-quarkonium dynamics in the quark-gluon plasma
due to the fact that the resulting inter-quark potentials are spatially
anisotropic, requiring real-time solution of the 3D Schr\"odinger equation.
Herein, we introduce a method for reducing anisotropic heavy-quark potentials
to isotropic ones by introducing an effective screening mass that depends on
the quantum numbers $l$ and $m$ of a given state. We demonstrate that, using
the resulting effective Debye screening masses, one can solve a 1D
Schr\"odinger equation and reproduce the full 3D results for the energies and
binding energies of low-lying heavy-quarkonium bound states to relatively high
accuracy. The resulting effective isotropic potential models could provide an
efficient method for including momentum-anisotropy effects in open quantum
system simulations of heavy-quarkonium dynamics in the quark-gluon plasma.
