- - 1: Explicitly construct the velocity operator from the momentum, vector-potential, and KB nonlocal-pseudopotential terms using two-center integral / spherical grid integral: $$\hat{v}_{\alpha}=-\mathrm{i}\nabla_{\alpha}+A_{\alpha}(t)+\mathrm{i}\left[\widetilde{V}_{\mathrm{NL}}^{\mathrm{KB}},r_{\alpha}\right],$$ where $\widetilde{V}_{\mathrm{NL}}^{\mathrm{KB}}=\mathrm{e}^{-\mathrm{i}\boldsymbol{A}(t)\cdot\boldsymbol{r}}\hat{V}_{\mathrm{NL}}^{\mathrm{KB}}\mathrm{e}^{\mathrm{i}\boldsymbol{A}(t)\cdot\boldsymbol{r}}$. $\boldsymbol{A}(t)$ is nonzero only for the velocity gauge (td_stype=1); otherwise $\boldsymbol{A}(t)=0$. Other nonlocal Hamiltonian terms (e.g., EXX) are not included explicitly.
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