QUANTITATIVE RECONSTRUCTION OF THE ELECTROSTATIC POTENTIAL IN MgO AND NaF BY ELECTRON AND X-RAY DIFFRACTION

A. Avilov¹, G. Lepeshov², A. Kulygin¹, V. Zavodnik³, E.Belokoneva⁴, V.Tsirelson², J.Stahn⁵, U.Pietsch⁵, J.Spence⁶

¹Institute of Crystallography Russian Acad.of Science, Moscow, Russia
²Quantum Chemisty Division, Mendeleev University, Moscow, Russia
³Karpov Physical-Chemical Institute, Moscow, Russia
⁴Moscow State University, Russia
⁵Institute of Physics, University of Potsdam, Germany
⁶Arizona State University, Phoenix , U.S.A.

Keywords: electrostatic potential, electron and X-ray diffraction

Electrostatic potential (EP) which is the main part of the crystal potential plays an important role in solid state physics and chemistry. It is an inherent part of the Schroedinger equation and reflects the nature of the interatomic interactions. Electron diffraction gives the structure factors which are Fourier-transforms of the inner-crystal thermal-smeared EP. We present an approach to extract the quasi-static EP from the accurate electron diffraction data.

It was possible using an improved electron diffractometer running in the transmission mode developed by our group. This diffractometer has been used to measure the structure factors for MgO ad NaF polycrystals. The quality of data was checked by comparing experimental structure factors received in kinematic approximation with ones from the non-empirical Hartree -Fock calculations for periodical crystals and with X-ray diffracton results. The letter ones were obtained by re-calculating the X-ray structure amplitudes to electron structure factors using the Mott-Bethe equation. In addition, several low-angle reflections were compared with those obtained with convergent-beam electron diffraction technique (CBED). The EP's were calculated using an analytical (-model adjusted to the experimental structure factors. The combination of data obtained by CBED and transmission technique allowed us to reduce the influence of extiction on the EP maps. The principal difference in the physical meaning of the model and Fourier EPs will be dicussed in detail.

Acknowledgements: The authors thank for support of the Russian Foundation for Basic Research, (N98-03-32654), the DFG-RFBI (N96-03-00071G and Pi218 13-1), and the CRDF (RP1-208). %