I feel like a ping pong ball on the question of whether or not total energy of a pair of electrons changes when they become entangled or disentangled. I began with a mental model similar to electrons in orbitals. Emit a photon and drop into a lower energy state until reading the ground state. A pair of electrons unentangled, emit and drop to the triplet state, then emit again and fall to the singlet (ground) state. In an earlier thread, CGK elegantly showed me how to write the Hamiltonian which does not include spin states, and the wavefuncitions which do include spin. In Quantum Mechanics, lecture 8, Leonard Susskind said that although entangled, there is nothing Bob can do that changes Alice's density matrix. If there was energy associated with entanglement, then if Bob became disentangled, it would change Alice's density matrix. (2) plus (3) convinced me that there can not be an energy change associated with enganglement/disentanglement. In Quantum Mechanics, Lecture 9, Susskind discussed an example. He started with an unentangled state |ud> and said that it could be expressed as a linear superposition |ud>= |singlet>+|triplet>. Then the pair could interact with a radiation field with states |0>=no photon, |1>=photon. Start with [|singlet>+|triplet>] ⊗ |0> which then evolves to |singlet | 0> + |singlet | 1> in which the triplet emits a photon and becomes a singlet. That brings me full circle again, in which the energy of the photon emited by the triplet is an energy delta. So, I can argue myself into both positions on this question, entanglement/disentanglement do [or do not] imply energy changes in the system. Help please! But going back to cgk's Hamiltonian, if there is energy associated with entanglement, why is there not a term for it in the Hamiltonian?