STATIC STRUCTURE FACTOR AND ELECTRON CORRELATION-EFFECTS STUDIED BY INELASTIC X-RAY-SCATTERING SPECTROSCOPY

Inelastic x-ray scattering spectra of methanol, acetonitrile, benzene, and cyclohexane have been measured with 2 eV resolution for momentum transfer q between 0.69 and 2.77 a.u. using synchrotron radiation from the photon factory (PF) storage ring. By utilizing the Bethe sum rule , the spectra were brought onto an absolute scale, so that the static structure factor S(q) has been obtained. S(q) of these molecules has a lso been calculated at the single reference configuration interaction (CI) with several types of basis sets. A new formula is proposed to ca rry out spherical averaging accurately. It is concluded that the CI si ngles and doubles (CISD) treatment is necessary to predict correct S(C I), and that an inclusion of polarization function influences S(q) sig nificantly at this level. An addition off functions also improves the agreement with the experiments. S(q)'s based on CISD wave functions ar e in good agreement with the experimental ones, in particular at large q. (C) 1998 American Institute of Physics.