When using plane wave basis functions,
what is the phase of each plane wave?
Should a one-electron wavefunction looks like $\Phi^k_{\beta}(r) = \sum_{G} c^k_{\beta,G}e^{i((k+G) r + \varphi_G)}$ instead of $\Phi^k_{\beta}(r) = \sum_{G} c^k_{\beta,G}e^{i(k+G) r}$?