Calculation of X-ray scattering intensities of molecules using density functional theory

The elastic and total intensities for X-ray scattering from the eighteen el ectron hydride series HCl, H2S, PH3, SiH4 are calculated from Kohn-Sham orb itals obtained using the B3LYP, BLYP and LSDA functionals. The elastic scat tering is compared to Hartree-Fock and SDCI calculations. The total scatter ing is compared to literature values at the SDCI level for H2S and MR-SDCI for SiH4. The elastic scattering appears to be accurate from DFT, although the lack of a highly correlated reference makes this conclusion a little in substantial due to the inadequacy of SDCI for larger molecules. The total s cattering is reasonably reproduced at small scattering angles and is good i n the tail region,but is qualitatively incorrect in the low (<2.5 a.u.) ran ge. The inelastic scattering of the isoelectronic molecule methanol (CH3OH) is also calculated from Kohn-Sham orbitals and compared to SDCI, CCSD and expe rimental results. For this quantity, DFT is no better than Hartree-Fock and much worse than SDCI and CCSD. (C) 2000 Elsevier Science B.V. All rights r eserved.