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