Abstract We consider the nonlinear Schrödinger equation with a harmonic potential in the presence of two combined energy‐subcritical power nonlinearities. We assume that the larger power is defocusing, and the smaller power is focusing. Such a framework includes physical models, and ensures that finite energy solutions are global in time. We address the questions of the existence and the orbital stability of the set of standing waves. Given the mathematical features of the equation (external potential and inhomogeneous nonlinearity), the set of parameters for which standing waves exist in unclear. In the two‐dimensional case, we adapt the method of fundamental frequency solutions, introduced by the second author in the higher‐dimensional case without potential. This makes it possible to describe accurately the set of fundamental frequency standing waves and ground states, and to prove its orbital stability.
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