R. N. Soguel, Аndrey Volotka, E. V. Tryapitsyna, D. A. Glazov, V. P. Kosheleva, S. Fritzsche, "Redefined vacuum approach and gauge-invariant subsets in two-photon-exchange diagrams for a closed-shell system with a valence electron", Physical Review A, vol. 103, 2021, [DOI: 10.1103/physreva.103.042818] [IF: 2.97, SJR: 1.18]