##### Electron density dictionary (rhoCIF) version 1.0.1

# _atom_local_axes_atom0

**Name:**

`'_atom_local_axes_atom0'`

**Definition:**

Specifies 'atom0' in the definition of a local axis frame. The definition employs three atom-site labels, 'atom0', 'atom1' and 'atom2', and two axis labels, 'ax1' and 'ax2', having values '+/-X', '+/-Y' or '+/-Z'. For the atom defined by '_atom_local_axes_atom_label', whose nuclear position is taken as the origin, local axis 'ax1' is the vector from the origin to atom0, axis 'ax2' is perpendicular to 'ax1' and lies in the plane of 'ax1' and a vector passing through the origin parallel to the vector atom1 -> atom2 (its positive direction making an acute angle with the vector parallel to atom1 -> atom2), and a right-handed orthonormal vector triplet is formed from the vector product of these two vectors. In most cases, atom1 will be the same as the atom specified by _atom_local_axes_atom_label. One or more 'dummy' atoms (with arbitrary labels) may be used in the vector definitions, specified with zero occupancy in the _atom_site_ description. The values of *_atom0, *_atom1 and *_atom2 must be identical to values given in the _atom_site_label list.

Appears in list containing _atom_local_axes_atom_label

**Must** match data name_atom_site_label

**Type:** char

**Category:** atom_local_axes