Theoretical Debye–Waller factors of α-MoO₃ estimated by an equation-of-motion method

EXAFS oscillations of MoO₃, which has a highly asymmetric local structure, have been calculated using backscattering amplitudes and phase shifts derived from the FEFF8 code and using Debye–Waller factors from an equation-of-motion method. They were compared with polarization-dependent empirical EXAFS data of the α-MoO₃ single crystal at various temperatures. The theoretical EXAFS oscillations of Mo—O bonds for the [001] direction of the single crystal, where two symmetric Mo—O bonds exist, reproduced well the experimental data. On the other hand, the calculated data for the [100] direction, which contain two asymmetric Mo—O bonds with different bond lengths, agree well with the experimental data only after adjustment of the amplitude reduction factors for different Mo—O bonds. EXAFS oscillations of MoO₃ powder were also calculated by the same method, and theoretical parameters that could reproduce the experimental data were found. These results suggest that the equation-of-motion method can evaluate the Debye–Waller factors efficiently in molecules with asymmetric local structures and can reduce curve-fitting parameters.