Research interests and publications Andrei Postnikov: selected topics and publications
from the complete publication list which is here.

    Ferroelectric systems, lattice instabilities, phonons:

    Alloys and intermetallics - electronic structure and interpretation of X-ray spectra:

    Magnetic molecules and small clusters:

    Defects and processes on the surface:

    Research interests and accomplishments

    Development of the quantitative theory of ferroelectricity and phase transitions in perovskite-type crystals

    By the beginning of 1990s, the development of full-potential calculation schemes allowed to simulate in a first-principles calculation and to analyze very delicate energy trends resulting in ferroelectric instability in some perovskite-type compounds. I performed pioneering works of this kind for KNbO3 and KTaO3 [28], concentrating later on on zone-center lattice dynamics [30, 32, 33] and the effects of hydrostatic pressure [35]. Later on, simulations have been done for Li-doped KTaO3, a dipole-glass system [42, 46], and for non-perovskite ferroelectrics of more complex structure, LiNbO3 [62] and LiTaO3 [77]. These calculations allowed to understand the details of chemical bonding and to extract the compositions of different phonon modes, the data not directly accessible in experiment (see, e.g., [65]).

    Contributions to the study of X-ray emission, inclusing resonant X-ray emission, in complex materials

    The analysis of photoelectron and X-ray emission spectra, especially when both are taken in combination from the same sample, can provide important information about the chemical bonding, degree of localization and the strength of correlation effects in different electronic states of a compound in question. However, in case of chemcally or structurally complex compounds the interpretation of the spectra may pose a problem. Calculations of electronic structure from first principles allows to reproduce X-ray spectral intensities and thus represent a powerful tool for analyzing experimental data. Such calculations have been done for a number of systems, including intermetallic compounds (many complex oxides, see e.g., [31, 36, 58, 54, 98]), thiospinels [67], La-based compounds [60]), diluted alloys (3d impurities in metals) and molecular crystals (Fe organophosphonate [73], "ferric wheel" [84], "ferric stars" [103, 102] ), using adequate (either tight-binding, or augmnented plane wave-based) calculation schemes.

    Studies of magnetism in intermetallic compounds, diluted and disordered alloys, and in small clusters/nanoparticles

    Magnetism in metallic systems (impurities, alloys etc.) was a substantial aspect of my research interests since the PhD work. By combining different theoretical approaches (KKR-CPA for fully disordered alloys [49, 81], Green's function approach for magnetic impurities [19, 13, 14], supercell band-structure calculations for partially ordered systems) one can get insight into the microscopics of local magnetic interactions. Often the motivation for the study of particular system was the need to explain experimental situation, e.g., photoelectron or X-ray emission spectra (3d-doped Ti dichalcogenides [70, 72, 99], ordered Mn superstructure on Cu [55]. In otrer cases, the simulation has been done in order to get information about microstructure not accessible experimentally (Fe nanoparticles [83]). The interplay between structural deformations (on the surface of a solid/cluster, or around the defects) and local magnetic properties has been looked at.