Normally, I think about orbitals interacting in the context of bonding. When two atomic orbitals overlap, they can do so in-phase or out-of-phase. The in-phase overlap results in a bonding molecular orbital with lower energy than the original AOs; conversely, the out-of-phase overlap results in an antibonding MO with higher energy. Valence electrons fill the bonding MOs first, resulting in a bond.
The explanation of steric effects that I often hear is that they are caused by the overlap of two electron clouds, resulting in repulsion. Since electron clouds are just composed of occupied orbitals, how is this "overlap of electron clouds" different from the picture of bonding I described above? Does the steric repulsion just come from occupied antibonding MOs? I imagine that inner shell electrons and Coulomb forces must play a role as well, right?
@matt_black answered a related question about steric vs eletronic effects by saying:
The normal distinction between "steric" and "electronic" is based on whether the effect is transmitted through space or through bonds
I guess I'm essentially asking a follow-up question on how effects are transmitted through space.