ATOM

Description

Defines an atom.

Syntax

ATOM label symbol x y z [B_iso] [occ] [mom] [charge]
The ATOM keyword requires five mandatory arguments: label, symbol, x, y, and z. The optional arguments, shown in brackets, are interpreted as follows. If six arguments are provided, the sixth is always interpreted as Biso. The seventh is interpreted as occ, the eighth as mom, and the ninth as charge. occ cannot be specified without specifying Biso, mom cannot be specified without specifying occ, and so on.

Arguments

label
Type: string
Atom label.
symbol
Type: string
Chemical symbol or scattering factor symbol. If Symbol refers to a scattering factor, there are three possible cases:
  • Neutron scattering length: the scattering factor symbol corresponds to the chemical symbol.
  • X-ray form factor: the scattering factor symbol is given by the chemical species (chemical symbol plus atomic charge), for instance AL, AL+3, F-1.
  • Magnetic form factor: the scattering factor symbols is M followed by the chemical symbol and the formal charge, for instance MFE0, MFE2. In the case of rare earths, two choices are available:
    • MHO3: magnetic form factor of Ho3+ as <j0>.
    • JHO3: magnetic form factor of Ho3+ as <j0> + c2<j2>.
x,y,z
Type: float
Atomic coordinates in reduced units.
Biso
Type: float
Isotropic atomic displacement parameter, Biso = 8π2⟨u2⟩, with ⟨u2⟩ being the mean square atomic displacement parameter.
occ
Type: float
Occupancy factor. For a crystallographic site with ocuppancy occ and multiplicity m, and M the general position multiplicity, the occupancy factor is calculated as occ · m / M.
mom
Type: float
Magnitude of the atomic magnetic moment, in bohr magneton.
charge
Type: float
Atomic charge.

Examples

  • Atom with chemical symbol and no optional arguments.

    ATOM   Fe  Fe  0.28220  0.25000  0.97410

  • Atom with chemical species symbol, two optional arguments and standard deviations.

    ATOM   Pb  PB+2  0.18749(10)  0.25000  0.16719(16)  1.42(3)  0.50000

  • Atom with magnetic form factor symbol and two optional arguments.

    ATOM   Ho_1  JHO3  0.28840  0.12500  0.11620  0.18451  0.50000