**Table 4:** Estimation of contribution spin-orbit (s-o), spin-other-orbit (s-o-o), spin-spin (s-s) and orbit-orbit (o-o) within shell interactions to energies for Fe XX levels within n=2 complex. $E_1=E^{{\rm s-o}}$ , $E_2=E^{{\rm s-o}}+E^{{\rm s-o-o}}$ , $E_3=E^{{\rm s-o}}+E^{{\rm s-o-o}}+E^{{\rm s-s}}$ and $E_4=E^{{\rm s-o}}+E^{{\rm s-o-o}}+E^{{\rm s-s}}+E^{{\rm o-o}}$ .
Index	E₁	E₂	E₃	E₄
2	141857	143122	143444	141910
3	182708	181082	181201	179270
4	264047	264411	264530	263975
5	327447	326489	326519	325670
6	755194	754560	754597	754662
7	821273	821367	821849	821936
8	843083	844242	843812	843945
9	1050595	1050928	1051144	1049976
10	1068168	1067125	1067206	1065988
11	1204074	1204221	1204372	1204963
12	1253448	1252420	1252540	1252569
13	1350217	1349293	1349347	1349601
14	1970331	1970400	1970517	1971268
15	2078969	2077652	2077773	2078527

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