Energy in quantum mechanics problems

[ntk]

I'm confused about choosing the value for energy in quantum mechanics problems such as in scattering, tunneling, boundstates.. problems because this affects later calculations. Given the potential in some regions, how do I decide energy to be negative or positive, or greater/less than the energy values?
Thank you very much

 

[nickjer]

If you want a bound state then you choose E less than the potential well (think of it classically were a particle is trapped in a well). If you want scattering then you choose E greater than (also think of it classically, where the particle can escape but it will be affected by the well).