# FIXED_ATOMS

Section can be repeated.

This section is used to constraint the fractional atomic position (X,Y,Z). Note that fractional coordinates are constrained, not real space coordinates. In case a restraint is specified the value of the TARGET is considered to be the value of the coordinates at the beginning of the run or alternatively the corresponding value in the section: FIX_ATOM_RESTART. [Edit on GitHub]

Subsections

- RESTRAINT

## Keywords

- COMPONENTS_TO_FIX

- EXCLUDE_MM

- EXCLUDE_QM

- LIST

- MM_SUBSYS

- MOLNAME

- QM_SUBSYS

## Keyword descriptions

COMPONENTS_TO_FIX: enum = XYZ

  Usage: COMPONENTS_TO_FIX (x|y|z|xy|xz|yz|xyz)

  Valid values:

  - `X` Fix only X component

  - `Y` Fix only Y component

  - `Z` Fix only Z component

  - `XY` Fix X-Y components

  - `XZ` Fix X-Z components

  - `YZ` Fix Y-Z components

  - `XYZ` Fix the full components of the atomic position.

  Mentions: ⭐Geometry Optimisation

  Specify which fractional components (X,Y,Z or combinations) of the atoms specified in the section will be constrained/restrained. [Edit on GitHub]

EXCLUDE_MM: logical = F

  Lone keyword: `T`

  Usage: EXCLUDE_MM <LOGICAL>

  Does not apply the constraint to the MM region within a QM/MM calculation. This keyword is active only together with MOLNAME [Edit on GitHub]

EXCLUDE_QM: logical = F

  Lone keyword: `T`

  Usage: EXCLUDE_QM <LOGICAL>

  Does not apply the constraint to the QM region within a QM/MM calculation. This keyword is active only together with MOLNAME [Edit on GitHub]

LIST: integer[ ]

  Keyword can be repeated.

  Usage: LIST {integer} {integer} .. {integer}

  Mentions: ⭐Geometry Optimisation

  Specifies a list of atoms to freeze. [Edit on GitHub]

MM_SUBSYS: enum = NONE

  Aliases: PROTEIN

  Usage: MM_SUBSYS (NONE|ATOMIC|MOLECULAR)

  Valid values:

  - `NONE` fix nothing

  - `ATOMIC` only the MM atoms itself

  - `MOLECULAR` the full molecule/residue that contains a MM atom (i.e. some QM atoms might be fixed as well)

  In a QM/MM run all MM atoms are fixed according to the argument. [Edit on GitHub]

MOLNAME: string[ ]

  Keyword can be repeated.

  Aliases: SEGNAME

  Usage: MOLNAME WAT MEOH

  Specifies the name of the molecule to fix [Edit on GitHub]

QM_SUBSYS: enum = NONE

  Usage: QM_SUBSYS (NONE|ATOMIC|MOLECULAR)

  Valid values:

  - `NONE` fix nothing

  - `ATOMIC` only the QM atoms itself

  - `MOLECULAR` the full molecule/residue that contains a QM atom (i.e. some MM atoms might be fixed as well)

  In a QM/MM run all QM atoms are fixed according to the argument. [Edit on GitHub]