page_title: Multipole density formalism
section_title: Applications
hierarchical_section_title: Multipole density formalism / Applications
caption_attribution_description: English: OH bond charge density resulting from Multipole Model refinement of doxycycline molecule, based of own data.
context_page_description: The Multipole Density Formalism is an X-ray crystallography method of electron density modelling proposed by Niels K. Hansen and Philip Coppens in 1978. Unlike the commonly used Independent Atom Model, the Hansen-Coppens Formalism presents an aspherical approach, allowing one to model the electron distribution around a nucleus separately in different directions and therefore describe numerous chemical features of a molecule inside the unit cell of an examined crystal in detail.
context_section_description: The primary advantage of the Hansen-Coppens formalism is its ability to free the model from spherical restraints and describe the surroundings of a nucleus far more accurately. In this way it becomes possible to examine some molecular features which would normally be only roughly approximated or completely ignored.
caption: Electron density isosurface map around a covalent bond modelled with the Multipole Model, with populational parameters taken from the ELMAM2 database. Note the elongated high-density area next to the hydrogen atom, pointing in the direction of oxygen.
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