Abstract. An easy to implement modulus-squared Dirichlet (MSD) boundary condition is formulated for numerical simulations of time-dependent complex partial differential equations in multidimensional settings. The MSD boundary condition approximates a constant modulus-squared value of the solution at the boundaries and is defined as 1. Introduction. When utilizing numerical methods to approximate the solutions to time-dependent partial differential equations (PDEs), proper handling of boundary conditions can be quite challenging. Sometimes, an otherwise stable numerical scheme will become unstable depending on how the boundary conditions are computed [42]. In addition, high-order schemes can degrade in accuracy to lower order when using boundary conditions which are not compatible with the high-order accuracy [26]. Proper handling of boundary conditions in higher-order schemes, especially in high-order compact schemes, can be even more of a challenge [19,20].Often, researchers will forgo a complicated boundary condition implementation and instead use tried-and-true boundary condition techniques which are very simple yet provide acceptable results. One of the most common is the use of Dirichlet boundary conditions when simulating solutions which decay towards zero at infinity, and where most of the dynamics (or "action") is expected to remain in the central regions of the computational grid. Another simple method in such cases is to use periodic boundary conditions.Infinite-domain problems involving PDEs whose function values are complex cannot, in general, make use of numerical Dirichlet or periodic boundary conditions because of the oscillation of the real and imaginary parts of the function due to the intrinsic frequency of the system. (In cases when both the real and imaginary parts of the solution converge to a constant at infinity, such boundary conditions can be