Question

How can a quantum particle be modelled by a wavepacket and a single wave function ?

Answer 1

\[\Psi(x,t) = \psi(x) e^{-iEt/\hbar}\]

Answer 2

Perhaps you made a mistake in your question, and what you meant to wonder is how a particle can be described by a wavepacket and a single energy eigenstate wavefunction, i.e. be in a state characterized by a definite energy. If THAT is what you're asking, the answer is that it can't. A wave packet is by definition not a stationary state, so it cannot be written as one energy eigenstate.