Electron-electron interaction Hamiltonian.

F = ham_ee(Sys)
F = ham_ee(Sys,eSpins)
F = ham_ee(Sys,eSpins,'sparse')

ham_ee returns the electron-electron interaction part of the spin Hamiltonian of the spin system given in Sys, in units of MHz.

If the vector eSpins is specified, only the interactions between the electron spins listed in eSpins is computed. For example, if eSpins = [1 3] and the spin system contains 3 electrons, only the interaction between electron spins 1 and electron 3 is returned. Otherwise, all electron spins are considered.

In the spin system structure, there are two ways to specify the electron-electron interactions: either via the field Sys.ee, or via Sys.J, Sys.dip, and Sys.dvec. To specify the orientation of the interaction matrix, use Sys.eeFrame.

If 'sparse' is given as third argument, the Hamiltonian matrix is returned in sparse format instead of full format.

For a two-electron system AB

AB.S = [1/2 1/2];
AB.g = [2 2.1];
AB.ee = [1 1 -2]*40;  % MHz

the electron-electron interaction Hamiltonian (in MHz) is

H = ham_ee(AB)

H =
    20     0     0     0
     0   -20   -20     0
     0   -20   -20     0
     0     0     0    20

E = eig(H)

E =
   -20
   -20
     0
    40

ham, ham_cf, ham_ez, ham_ezho, ham_hf, ham_nn, ham_nq, ham_nz, ham_oz, ham_so, ham_zf