Right now GradDDFT implements the original expression for the LYP functional, eq 22 in
Lee, Yang & Parr
C. Lee, W. Yang, and R. G. Parr., Phys. Rev. B 37, 785 (1988) (doi: 10.1103/PhysRevB.37.785)
but there is a more computationally efficient one, eq 2 in
B. Miehlich, A. Savin, H. Stoll, and H. Preuss., Chem. Phys. Lett. 157, 200 (1989) (doi: 10.1016/0009-2614(89)87234-3)
This is low priority however.
Right now GradDDFT implements the original expression for the LYP functional, eq 22 in
but there is a more computationally efficient one, eq 2 in
This is low priority however.