V. 2 p$_{j}$ − 2 s TRANSITION ENERGIES IN LI-LIKE IONS 30 In this section, we collect all theoretical contributions available for the 2 p$_{1}$$_{/}$$_{2}$ − 2 s and 2 p$_{3}$$_{/}$$_{2}$ − 2 s transition energies for middle- Z Li-like ions, compare them with experimental results, and discuss prospects for further improvement of the theoretical accuracy. Individual contributions to the 2 p$_{1}$$_{/}$$_{2}$ − 2 s and 2 p$_{3}$$_{/}$$_{2}$ − 2 s transition energies are presented in Tables X and XI, respectively. The rms radii and their uncertainties are listed in the second column of the tables. These values are taken from Ref. [56]. The uncertainty of the electronic-structure values includes an error due to the model-dependence of the nuclear charge distribution. It is conservatively estimated by comparing the results obtained within the Fermi and the homogeneously charged-sphere model. Except for neon ( Z = 10), the electronic-structure contributions given are obtained in this work. In case of neon, we use the related result of Ref. [48], which has a higher accuracy. Next, one should take into account the first-order one-electron QED corrections. They are determined by the SE and the VP. The SE correction is obtained by interpolating the values presented in Ref. [68] for the 2 s and 2 p$_{1}$$_{/}$$_{2}$ states and in Ref. [69] for the 2 p$_{3}$$_{/}$$_{2}$ state. The Uehling part of the VP contribution was calculated in the present work while the Wichmann-Kroll part is taken from Ref. [70]. The next corrections, which caused the largest theoretical uncertainties for middle- Z ions [13], are the nuclear recoil and screened QED contributions. The recoil effect is considered in Sec. II, while the evaluation of the screened QED corrections is presented in Sec. IV. These calculations improve considerably the accuracy of the theoretical predictions for the 2 p$_{j}$ − 2 s transition energies in middle- Z Li-like ions. Finally, we should account for the two-loop one-electron QED effect. So-called “SEVP”, “VPVP”, and “S(VP)E” subsets were recently tabulated in Ref. [15]. The remaining two- loop SE correction (the “SESE” subset) for n = 2 states was accomplished only for several ions with Z ≥ 60 [12]. In order to obtain the SESE correction for middle- Z ions we use an extrapolation procedure. For the 2 s state, the extrapolation is performed in two steps. At first, the numerical values for the 1 s state are obtained by interpolating the numerical results of Refs. [12, 71, 72]. Then the weighted difference Δ$_{s}$ = 8 δE$_{2}$$_{s}$ − δE$_{1}$$_{s}$ is achieved by using low-order terms of the αZ -expansion and extrapolating the higher-order contributions from the all-order results (see Ref. [73] and references therein). An uncertainty of 30% is assigned