ν = 1 2 ∑ σ σ ′ ∫ d 3 r d 3 r ′ v ( r → − r ′ → ) ψ σ {\displaystyle \nu ={\frac {1}{2}}\sum _{\sigma \sigma ^{\prime }}\int d^{3}rd^{3}r^{\prime }v({\vec {r}}-{\vec {r^{\prime }}})\psi _{\sigma }}
