From Eq. (17) one can see that for the first-order self-energycorrection the divergent part is zero. However, in case of the higher-order diagrams under consideration the contributions of par- ticular diagrams are divergent. Nevertheless, as it is shown below, the sum of all the contributions to the screened self-energy correction is finite. The irreducible parts of the diagrams A , B and E can be presented as the matrix elements of the self-energy operator 〈 X | Σ( ε ) | Y 〉 with various wave functions 〈 X | and | Y 〉 . The formulas for these contributions are as follows, A. ”Modified self-energy” diagrams Δ E SE( A ) SQED = Δ E SE( A 1) SQED + Δ E SE( A 2) SQED , (19) Δ E SE( A 1) SQED = 2 ∑ n 1 , 2 $^{′}$〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉 〈 n$_{1}$ | T$_{0}$ | n$_{2}$ 〉〈 n$_{2}$Pb | I (Δ) | QaQb 〉 ( ε$_{Pa}$ − ε$_{n}$$_{1}$ )( ε$_{Pa}$ − ε$_{n}$$_{2}$ ) , (20) Δ E SE( A 2) SQED = 2 ∑ n 1 , 2 $^{′}$〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉 〈 n$_{1}$Pb | I (Δ) | n$_{2}$Qb 〉〈 n$_{2}$ | T$_{0}$ | Qa 〉 ( ε$_{Pa}$ − ε$_{n}$$_{1}$ )( ε$_{Qa}$ − ε$_{n}$$_{2}$ ) , (21) Δ E SE( B ) SQED = 2 ∑ n 1 , 2 ′ 〈 Pa | T$_{0}$ | n$_{1}$ 〉 ε$_{Pa}$ − ε$_{n}$$_{1}$ 〈 n$_{1}$ | Σ( ε$_{Pa}$ ) | n$_{2}$ 〉 〈 n$_{2}$Pb | I (Δ) | QaQb 〉 ε$_{Pa}$ − ε$_{n}$$_{2}$ , (22) Δ E SE( E ) SQED = Δ E SE( E 1) SQED + Δ E SE( E 2) SQED , (23) Δ E SE( E 1) SQED = 2 ∑ n 1 , 2 $^{′}$〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉 〈 Pb | T$_{0}$ | n$_{2}$ 〉〈 n$_{1}$n$_{2}$ | I (Δ) | QaQb 〉 ( ε$_{Pa}$ − ε$_{n}$$_{1}$ )( ε$_{Pb}$ − ε$_{n}$$_{2}$ ) , (24) Δ E SE( E 2) SQED = 2 ∑ n 1 , 2 $^{′}$〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉 〈 n$_{1}$Pb | I (Δ) | Qan$_{2}$ 〉〈 n$_{2}$ | T$_{0}$ | Qb 〉 ( ε$_{Pa}$ − ε$_{n}$$_{1}$ )( ε$_{Qb}$ − ε$_{n}$$_{2}$ ) . (25) Δ E SE( G ) SQED = Δ E SE( G 1) SQED + Δ E SE( G 2) SQED + Δ E SE( G 3) SQED , (26) Δ E SE( G 1) SQED = − 2 ∑ n 1 ′ 1 ( ε$_{Pa}$ − ε$_{n}$$_{1}$ ) 2 [ 〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉〈 n$_{1}$ | T$_{0}$ | Pa 〉〈 PaPb | I (Δ) | QaQb 〉 + 〈 Pa | Σ( ε$_{Pa}$ ) | n$_{1}$ 〉〈 n$_{1}$Pb | I (Δ) | QaQb 〉〈 Pa | T$_{0}$ | Pa 〉 + 〈 Pa | Σ( ε$_{Pa}$ ) | Pa 〉〈 Pa | T$_{0}$ | n$_{1}$ 〉〈 n$_{1}$Pb | I (Δ) | QaQb 〉 ] , (27) 8 All the reducible terms of the similar structure are denoted as Δ E SE( G ) $_{SQED}$,