V ( λ ) = λα ∑ i>j [ 1 r$_{ij}$ − α i · α j 2 r$_{ij}$ − ( α i · r$_{ij}$ )( α j · r$_{ij}$ ) 2 r 3 ij ] , (11) E ( λ ) = E$_{0}$ + E$_{1}$λ + E$_{2}$λ 2 + ∞ ∑ k =3 E$_{k}$λ $^{k}$, (12) evaluations of these contributions within the Breit approximation are generally sufficient. Previously such calculations for Li-like ions were performed in Refs. [7, 9, 10, 13]. The evaluations of Refs. [7, 10] were carried out with the hydrogenic wave functions while in Refs. [9, 13, 52] the perturbation expansion starts with a local screening potential, which partly incorporates the electron-electron interaction effects. In the present investigation, to evaluate the interelectronic-interaction corrections of the third and higher orders we proceed as follows. The large-scale CI-DFS method (see, e.g., Refs. [34, 38]) was used to solve the Dirac-Coulomb-Breit equation yielding the energies. The operator of the interelectronic interaction in the Breit approximation reads where a scaling parameter λ is introduced to separate terms of different order in 1 /Z using the numerical results obtained for different values of λ . Thus, for small λ , the total energy of the system can be expanded in powers of λ E$_{k}$ = 1 k ! d k d λ $_{k}$E ( λ ) ∣ λ $_{=0}$. (13) E ⩾ 3 = E ( λ = 1) − E$_{0}$ − E$_{1}$ − E$_{2}$, The higher-order contribution E ⩾ 3 ≡ ∑ ∞ k $_{=3}$E$_{k}$ is calculated as where the terms E$_{0}$ , E$_{1}$ , and E$_{2}$ are determined numerically according to Eq. (13). The results of the numerical calculation of the higher-order interelectronic-interaction contribu- tions for the 2 p$_{1}$$_{/}$$_{2}$ -2 s and 2 p$_{3}$$_{/}$$_{2}$ -2 s transition energies in Li-like ions are collected in Table VI. “C” in the second column indicates that only Coulomb interaction is taken into account, while “C+B” means that both Coulomb and Breit interactions are included. As one can see from the table, in accordance with Refs. [7, 13], the Breit interaction contribution is rather significant, especially for middle and high- Z ions. We note that the third-order con- tribution monotonously increases and changes the sign when Z increases. The uncertainty of the results consists of two parts: an uncertainty due to some approximations made in the numerical procedure, in the table it is written in the first brackets, and an uncertainty due to the Breit approximation, it is given in the second brackets. To estimate the first 14