Research interests and publications
Andrei Postnikov: selected topics and publications

from the complete publication list which is here.
### Ferroelectric systems, lattice instabilities, phonons:

- A. V. Postnikov, T. Neumann, G. Borstel and M. Methfessel.

Ferroelectric structure of KNbO_{3}
and KTaO_{3} from first-principles calculations.

*Phys. Rev. B* **48**, 5910 (1993). -
This is also my most cited publication, 58 times
according to the *Web of Science*.

- V. Caciuc, A. V. Postnikov and G. Borstel.

*Ab initio* structure and zone-center phonons in LiNbO_{3}.

*Phys. Rev. B* **61**, 8806 (2000).

- A. V. Postnikov, O. Pagès and J. Hugel.

Lattice dynamics of mixed semiconductors (Be,Zn)Se
from first-principles calculations.

*Phys. Rev. B* **71**, 115206 (2005).

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

- A. Moewes, A. V. Postnikov, E. Z. Kurmaev, M. M. Grush and D. L. Ederer.

Resonant mixing of widely separated intermediate states and charge
transfer at the 4d-4f resonance of La compounds.

*EuroPhys. Lett.* **49**, 665 (2000).

- A. N. Titov, A. V. Kuranov, V. G. Pleschev, Y. M. Yarmoshenko, M. V.
Yablonskikh, A. V. Postnikov, S. Plogmann, M. Neumann, A. V. Ezhov and E. Z.
Kurmaev.

Electronic structure of Co_{x}TiSe_{2}
and Cr_{x}TiSe_{2}.

*Phys. Rev. B* **63**, 035106 (2001).

- N. I. Kulikov, D. Fristot, J. Hugel and A. V. Postnikov.

Interrelation between structural ordering and magnetic properties in
bcc Fe-Si alloys.

Phys. Rev. B **66**, 014206 (2002)

### Magnetic molecules and small clusters:

- L. D. Finkelstein, A. V. Postnikov, E. Z. Kurmaev, M. Matteucci, G. Robert,
B. Schneider, M. Neumann and C. Bellitto.

Inelastic X-ray scattering measurements of iron organophosphonate.

Phys. Rev. B **63**, 075113 (2001).

- A. V. Postnikov, P. Entel and J. M. Soler.

Density functional simulation of small Fe nanoparticles.

*Eur. Phys. J. D* **25**, 261 (2003).

- A. V. Postnikov, G. Bihlmayer and S. Blügel.

Exchange parameters in Fe-based molecular magnets.

*Comput. Mater. Sci.* **35**, No. 5, ??? (2006).

### Defects and processes on the surface:

- F. Pforte, A. Gerlach, A. Goldmann, R. Matzdorf,
J. Braun and A. Postnikov.

Wave-vector dependent symmetry analysis of a photoemission matrix element:
the quasi-1D model system Cu(110)(2x1)O.

*Phys. Rev. B* **63**, 165405 (2001).

- J. Braun, C. Math, A. Postnikov and M. Donath.

Surface resonances versus surface states on Fe(110).

*Phys. Rev. B* **65**, 184412 (2002).

- A. Robin, A. Postnikov and W. Heiland.

Electronic stopping of keV nitrogen ions interacting
with a Pt(100)(1x2) surface - a tool to characterize
electronic surfaces.

*Surf. Interph. Analysis* **37**, 154 (2005).

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 KNbO_{3} and KTaO_{3}
[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 KTaO_{3}, a dipole-glass system
[42,
46],
and for non-perovskite ferroelectrics of more
complex structure, LiNbO_{3}
[62]
and LiTaO_{3}
[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.