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

Abstract

The elastic and total intensities for X-ray scattering from the eighteen electron hydride series HCl, H 2S, PH 3, SiH 4 are calculated from Kohn–Sham orbitals obtained using the B3LYP, BLYP and LSDA functionals. The elastic scattering is compared to Hartree–Fock and SDCI calculations. The total scattering is compared to literature values at the SDCI level for H 2S and MR-SDCI for SiH 4. The elastic scattering appears to be accurate from DFT, although the lack of a highly correlated reference makes this conclusion a little insubstantial due to the inadequacy of SDCI for larger molecules. The total scattering is reasonably reproduced at small scattering angles and is good in the tail region, but is qualitatively incorrect in the low (<2.5 a.u.) range. The inelastic scattering of the isoelectronic molecule methanol (CH 3OH) is also calculated from Kohn–Sham orbitals and compared to SDCI, CCSD and experimental results. For this quantity, DFT is no better than Hartree–Fock and much worse than SDCI and CCSD.