\psi*\nabla\psi-\psi\nabla\psi*=-\frac{i}{(2\pi)^6}\int_{\mathbb{R}^3}\int_{\mathbb{R}^3}(\vec{k}'+\vec{k})\mathrm{e}^{i\vec{a}(\vec{k}'-\vec{k})}\mathrm{e}^{-i\vec{r}(\vec{k}'-\vec{k})}d^3\vec{k}d^3\vec{k}'