Interaction induced accelerating motion of initial steady Gaussian BEC wave packets (13). In panels (a1)–(a4), (b1)–(b4), and (c1)–(c4), the interactions are set to be (a1) Ng(x) = 0.3(x + 10), (b1) −0.3(x+10), and (c1) −3, respectively. Panels (a2)–(c2), (a3)–(c2), and (a4)–(c4) show the evolution of BEC density |ψ(x,t)|², mean values of wave packet position ⟨x⟩ and acceleration a defined by Eq. (3), respectively. {In (b4), the dashed line represents the FWHM of the wave packet.} All the three initial wave packets have the same parameters σ₀ = 1 and x₀ = 0.