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The form and electronic structure of the valence band (VB) of the ferroelectric SbSI crystal was calculated by solving the Hartree-Fock-Roothaan matrix equation. The diagonal eigenvalue matrix ε gives the electron state energies. These energies were also studied experimentally by PHI 5700 / 660 Physical Electronics Spectrometer using Al Kα monochromatic radiation (1486.6 eV) as the excitation source. The spectrum of the VB electronic levels was approximated by the Gauss functions. The form of the VB depends on the width of the Gauss function and the number of SbSI molecules, which were taken into account in the model of SbSI crystal. The obtained theoretical density of states and the VB form of SbSI crystal is close to the experimental one.

The paper presents the results of theoretical calculations of the shifts of Bi and Sb X-ray photoelectron spectra (XPS) due to chemical bond formation in Bi2S3 and Sb2S3 crystals. The energies of core levels of Bi, Sb, and S atoms are calculated by both the Hartree-Fock-Dirac (HFD) and Hartree-Fock methods and compared with the experimental values. The HFD method explains well the experimentally obtained spin-orbit splitting of the XPS. However, both theoretical methods give higher negative core level energies than their experimental values are.

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) from the (010) and (001) plane axes for the quasi-one-dimensional TlInSe2 single crystal. The XPS were measured with monochromatized Al Kα radiation in the energy range of 0-1400 eV at room and 393 K temperature. The VB is located 0.6-10 eV below the Fermi level. Experimental energies of the VB and CL are compared with the results of quantum mechanical ab initio calculations of the molecular model of the TlInSe2 crystal. The electronic structure of the VB and CL is described theoretically by quantum mechanical Hartree-Fock calculations. The surface and bulk atoms influence the shape of the VB and CL, which is crystallographic plane dependent. The chemical shifts in the TlInSe2 crystal for the Tl, In, and Se states are obtained.