Crystallographic cell converter

Nicolas Schoeni and Gervais Chapuis
École Polytechnique Fédérale de Lausanne, Switzerland

It is often necessary to describe a crystal structure in a new unit cell different from the original.

If a, b and c are the lattice vectors defining the unit cell, the new lattice vectors a’, b’ and c’ are obtained from the following matrix transformation P

where P is the matrix

In some cases, the new origin of the unit cell is not identical to the old one. The origin shift is given by the column vector

In the new unit cell, the atomic coordinates are given by the following relation



In the absence of a CIF file, the user can select on the existing one in the menu and edit the file ignorer to introduce the original lattice constants. The P and p arrays can introduced in the applet along wth the atomic coordinates. After transformation a new CIF file is created with the new atomic coordinates referring to the new unit cell.