5 B. Method of calculation H$_{RSMS}$ = − 1 2 M ∑ i = j αZ r$_{i}$ [ α i + ( α i · r$_{i}$ ) r$_{i}$ r 2 i ] · p$_{j}$ , (4) Δ E = 〈 ψ | H$_{M}$ | ψ 〉 ≡ K/M, (5) where “RNMS” stays for the relativistic NMS. The corresponding two-electron correction is where “RSMS“ denotes the relativistic SMS. The recoil correction to a given atomic state to first order in m/M is obtained as the expectation value of H$_{M}$ on the Dirac wave function (here and in what follows, the Dirac wave functions are the eigenvectors of the Dirac-Coulomb-Breit Hamiltonian). In Ref. [33] the Hamiltonian (2) was employed to calculate the ( αZ ) $^{4}$m/M corrections to the energy levels in He- and Li-like ions to zeroth order in 1 /Z . Later in Refs. [34, 35], this Hamiltonian was used to evaluate the relativistic recoil effect in low- and middle- Z ions and atoms to all orders in 1 /Z . The recoil correction of the first order in m/M is conveniently expressed in terms of the constant K defined by The recoil correction which is beyond the Breit approximation (2) is referred to a QED recoil effect. This effect has to be also taken into account, especially for high- Z ions. For H- and Li-like ions the QED recoil corrections have been calculated to all orders in αZ and to zeroth order in 1 /Z in Refs. [36, 37]. In what follows, we focus on the calculations of the coefficient K to all orders in 1 /Z for the 2 p$_{j}$ − 2 s transitions in a wide range of Li-like ions. We investigate relative contributions of the relativistic and QED corrections to the total recoil effect and the influence of the electron correlations on the recoil effect. where | ψ 〉 is the eigenvector of the Dirac-Coulomb-Breit Hamiltonian. With this constant, the mass isotope shift for two different isotopes with nuclear masses M$_{1}$ and M$_{2}$ can be written as δE = K ( 1 M 1 − 1 M 2 ) . Expectation values of the MS operator (2) are very sensitive to the electron correlations. In the present investigation the large-scale configuration-interaction (CI) Dirac-Fock-Sturm (DFS) method was employed to solve the Dirac-Coulomb-Breit equation with high accu- racy. This method was developed by Tupitsyn and partially presented in Ref. [38]. It was