# Core CIF Dictionary version 2.3

# _geom_hbond_site_symmetry_

### Names

`'_geom_hbond_site_symmetry_D'`
`'_geom_hbond_site_symmetry_H'`
`'_geom_hbond_site_symmetry_A'`
**Category:** geom_hbond

**Data type:** char

**Must** appear in a looped list
containing `'_geom_hbond_atom_site_label_'`

**Examples:**

. 'no symmetry or translation to site'

4 '4th symmetry operation applied'

7_645 '7th symm. posn.; +a on x; -b on y'

### Definition

The symmetry code of each atom site as the symmetry-equivalent
position number 'n' and the cell translation number 'klm'.
These numbers are combined to form the code 'n klm' or n_klm.
The character string n_klm is composed as follows:
n refers to the symmetry operation that is applied to the
coordinates stored in _atom_site_fract_x, _atom_site_fract_y
and _atom_site_fract_z. It must match a number given in
_symmetry_equiv_pos_site_id.
k, l and m refer to the translations that are subsequently
applied to the symmetry transformed coordinates to generate
the atom used in calculating the hydrogen bond. These
translations (x,y,z) are related to (k,l,m) by the relations
k = 5 + x
l = 5 + y
m = 5 + z
By adding 5 to the translations, the use of negative numbers
is avoided.

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