TY - JOUR

T1 - Theoretical calculation of the time-averaged electron density distribution for vibrating ethyne molecules in a model crystal structure

AU - Ruysink, A. F. J.

AU - Vos, A.

PY - 1974

Y1 - 1974

N2 - Calculations have been made on an ethyne model structure to investigate the influence of internal and external thermal motions of the molecules in a crystal on the time-averaged electron density distribution as obtained by X-ray diffraction. The density distributions in the chemical bonds have been studied from D(r) = Q(mol, r)-Q(at, r) difference maps, where Q(at, r) is the density of the free-atom structure. Vibrations expected to occur at low temperatures reduce the difference densities at the centres of the C-C and C-H bonds by 12 and 23% respectively. Reliable time-averaged difference density distributions can be calculated from the static distributions obtained by theory by use of the root-mean-square deviations (u2)1/2 of the atoms which can be determined by X-ray diffraction. Only negligibly small errors occur in the theoretical difference density maps if librations are accounted for by linear vibrations. In the experimental [Fo-Fc] difference densities errors due to treating librations as linear vibrations are largely, but not completely, compensated by shifts of the atoms.

AB - Calculations have been made on an ethyne model structure to investigate the influence of internal and external thermal motions of the molecules in a crystal on the time-averaged electron density distribution as obtained by X-ray diffraction. The density distributions in the chemical bonds have been studied from D(r) = Q(mol, r)-Q(at, r) difference maps, where Q(at, r) is the density of the free-atom structure. Vibrations expected to occur at low temperatures reduce the difference densities at the centres of the C-C and C-H bonds by 12 and 23% respectively. Reliable time-averaged difference density distributions can be calculated from the static distributions obtained by theory by use of the root-mean-square deviations (u2)1/2 of the atoms which can be determined by X-ray diffraction. Only negligibly small errors occur in the theoretical difference density maps if librations are accounted for by linear vibrations. In the experimental [Fo-Fc] difference densities errors due to treating librations as linear vibrations are largely, but not completely, compensated by shifts of the atoms.

U2 - 10.1107/S0567739474001197

DO - 10.1107/S0567739474001197

M3 - Article

VL - A 30

SP - 497

EP - 502

JO - Acta Crystallographica Section A

JF - Acta Crystallographica Section A

SN - 0108-7673

ER -