where L OOCCD is the OO-CCD Lagrangian. This leads to the orbital-optimized coupledcluster doubles equations, which include both the doubles amplitude equations and the orbital rotation equations. Solving these equations self-consistently provides the OO-CCD energy as well as a reference determinant with optimized orbitals. This optimized reference determinant can then be used to obtain an electron density according to Eq. ( ) as well as the corresponding Coulomb potential.