Build a Bloch-conditioned neural model whose periodic-factor representation transforms covariantly when the supplied Bloch wavenumber is shifted by a reciprocal lattice vector. Either canonicalize q to the first Brillouin zone or augment training with mathematically paired examples whose outputs differ by the exact phase gauge. This prevents the network from learning inconsistent predictions for physically identical Bloch modes.
For neural eigenmode solvers on periodic domains, train the full field directly and impose Bloch phase coupling only at opposite cell boundaries, rather than differentiating a periodic factor with respect to q through a quadratic volume operator. The boundary formulation preserves reciprocal-lattice equivalence exactly through z=exp(iqa), reducing spurious eigenmodes caused by inconsistent q-dependent discretization.