# ATOM_GROUP

Section can be repeated.

Define a group of atoms for use in a CDFT constraint. Each repetition of this section creates a new constraint. [Edit on GitHub]

## Keywords

- ATOMS

- COEFF

- CONSTRAINT_TYPE

- FRAGMENT_CONSTRAINT

## Keyword descriptions

ATOMS: integer[ ]

  Usage: ATOMS {integer} {integer} .. {integer}

  Mentions: ⭐Constrained DFT

  Specifies the list of atoms that are included in the constraint group. [Edit on GitHub]

COEFF: real[ ]

  Keyword can be repeated.

  Usage: COEFF 1.0 -1.0

  Mentions: ⭐Constrained DFT

  Defines coefficients for the atoms in the list of atoms. Accepts values +/-1.0. [Edit on GitHub]

CONSTRAINT_TYPE: enum = CHARGE

  Usage: CONSTRAINT_TYPE (CHARGE|MAGNETIZATION|ALPHA|BETA)

  Valid values:

  - `CHARGE` Total charge density constraint (rho_alpha + rho_beta).

  - `MAGNETIZATION` Magnetization density constraint (rho_alpha - rho_beta).

  - `ALPHA` Alpha spin density constraint.

  - `BETA` Beta spin density constraint.

  Mentions: ⭐Constrained DFT

  Determines what type of constraint to apply. [Edit on GitHub]

FRAGMENT_CONSTRAINT: logical = F

  Lone keyword: `T`

  Usage: FRAGMENT_CONSTRAINT

  Mentions: ⭐Constrained DFT

  Use a fragment based constraint. Takes as input the electron densities of two isolated fragments in the same geometry that they have in the full system. The isolated fragment densities are read from cube files defined in FRAGMENT_{A,B}FILE. For magnetization density constraints, additional files containing the spin difference densities must be defined with the keywords FRAGMENT{A,B}_SPIN_FILE. With this keyword active, the target value of the constraint is calculated from the the superposition of the isolated fragment densities. Supports only static calculations. [Edit on GitHub]