Beyond the Fermi pseudopotential: A modified Gross-Pitaevskii equation

We present an effective potential and the corresponding modified Gross-Pitaevskii equation, which account for the energy dependence of the two-body scattering amplitude through an effective-range expansion. For the ground-state energy of a trapped condensate, the theory leads to what we call a shape-dependent confinement correction that improves agreements with diffusion Monte Carlo calculations. The theory illustrates, for relatively strong confinement and/or high density, how the shape dependence on atom-atom interaction can come into play in a many-atom quantum system.