Nowadays, the most routine X-ray structure determination in crystallography is based on so-called Independent Atom Model (IAM) of electron density, which assumes both sphericity and neutrality of the atoms. Unfortunately, the quantitative topological analysis of an electron density based on IAM is inaccessible (Dittrich *et al.*, 2009). The multipolar approach, as proposed by Hansen and Coppens (Coppens, 1997)^{ }, is the method of choice in modelling of the experimental electron density distribution. High-resolution diffraction data of outstanding quality are mandatory in order to perform full structure refinement with multipolar model – a condition impossible to meet for very small crystals or macromolecules. However, the theoretical databanks of aspherical scattering factors developed in recent years, for example, UBDB databank (Jarzembska & Dominiak, 2012) based on experimental geometries, can be used in order to reconstruct the charge density with the Transferable Aspherical Atom Model (TAAM) approach.

Acridines belong to the polycyclic heteroaromatic chemical compounds and their derivatives have found a wide range of applications in clinical area as an antimicrobial, antiviral or antitumor agents as well as in chemical analysis, for example as a matrix for matrix-assisted laser desorption/ionization (MALDI). The 9-aminoacridine can be considered as a model compound from this family of chemicals. In its neutral form it crystallizes as a hemihydrate the *I *4_{1}/*a* 2/*c* 2/*d* space group with several atoms in special positions. The very interesting crystal structure of title compound was described in the 1983 year by Chaudhuri and until now has not been more thoroughly investigated. Here, the reconstruction of charge density distribution with the UBDB data bank and TAAM refinement will be performed in order to obtain more accurate geometry of the compound, the quantitative topological analysis of an electron density as well as the basis for the energetic calculation (crystal lattice and dimer energies) by using *Crystal*, *CrystalExplorer* or *Pixel* approaches. This research is the part of the wider project carried out in cooperation with dr Mihails Arhangelskis.

Acknowledgments:

Polish National Science Centre MAESTRO grant decision number DEC2012/04/A/ST5/00609, DSM grant No. 501-D112-86-DSM-115 100 are acknowledged.

Coppens, P. (1997). X-Ray Charge Densities and Chemical Bonding; International Union of Crystallography.

Dittrich, B.; Weber, M.; Kalinowski, R.; Grabowsky, S.; Hübschle, C. B.; Luger, P. (2009). Acta Crystallogr. 65 (6), 749–756.

Jarzembska, K. N.; Dominiak, P. M. (2012). Acta Crystallogr. A. 68 (Pt 1), 139–147.

Keywords: 9-aminoacridine hemihydrate, charge density, TAAM refinement