No source-free exchange-correlation magnetic fields in non-collinear spin DFT
We show that the Maxwellian equation $\nabla\cdot\mathbf{B}_{\mathrm{xc}}=0$, where $\mathbf{B}_{\mathrm{xc}}$ is the exchange-correlation (xc) magnetic field, is not an exact condition of non-collinear spin density functional theory: it violates global spin-rotation symmetry, the operation which turns the electron spins. How much...