title: Differential geometry: a natural tool for describing symmetry operations.
abstract: Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications.
authors.affiliation: Laboratoire de Cristallographie, IPMC-FSB, Ecole Polytechnique Fédérale de Lausanne, BSP-Le Cubotron, Dorigny, CH-1015 Lausanne, Switzerland. philippe.kocian@epfl.ch
authors.forename: Philippe
authors.initials: P
authors.lastname: Kocian
authors.forename: Kurt
authors.initials: K
authors.lastname: Schenk
authors.forename: Gervais
authors.initials: G
authors.lastname: Chapuis