The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT. The hybrid functional method correctly describes the spectrum of the valence and conduction bands however, the HOMO-LUMO gap width is significantly underestimated. This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H2Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications.
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