MS22-P01 HAR and TAAM Refinements of Model Crystal Structures using CuKα and MoKα X-ray Diffraction DataCommonly, the Independent Atom Model (IAM) of electron density is used in the case of routine X-ray data analysis. However, this model does not give a quantitative description of electron density distribution because atoms are assumed to be neutral and spherical. A far better model that allows for modelling of deformation of spherical charge density was introduced by Hansen and Coppens1 and is called a pseudoatom model of electron density. Application of this kind of model requires an excellent quality crystals and high resolution XRD data. Quite often, this is difficult to be fulfilled. Therefore, new methods have been developed that enable reconstruction of electron density i.e. Hirshfeld Atom Refinement (HAR)2 or Transferable Aspherical Atom Model (TAAM)3.
Validation of application of HAR and TAAM methods for low-resolution data will be presented. For three compounds following refinements of CuKα and MoKα data will be presented: IAM, TAAM (isotropic H atoms), TAAM (using Shade), HAR (isotropic H atoms), HAR (anisotropic H atoms), HAR (using Shade). Additionally, the multipole model and higher order of TAAM and HAR refinements will be presented for MoKα X-ray diffraction data. Analysis of geometry, ADPs (Fig. 1), fractal dimension plots and residual density maps will be shown in comparison with neutron diffraction data.
Fig.1 PEANUT representations of the difference between ADPs obtained from neutron data refinement and HAR, TAAM refinements for MoKα and CuKα data. Root mean square difference scale of 2 was used.References:
 Hansen, N. K.; Coppens, P. (1978). Acta Crystallogr. A. 34 (6). 909–921.
Capelli, S. C.; Bürgi, H.-B.; Dittrich, B.; Grabowsky, S.; Jayatilaka, D. (2014). IUCrJ. 1 (5). 361–379.
 Jarzembska, K. N.; Dominiak, P. M. (2012).. Acta Crystallogr. A. 68 (1). 139–147.Keywords: Hirshfeld Atom Refinement, Transferable Aspherical Atom Model, charge density