Section CELL_OPT

• This section sets the environment for the optimization of the simulation cell. Two possible schemes are available: (1) Zero temperature optimization; (2) Finite temperature optimization.

• Section path: CP2K_INPUT / MOTION / CELL_OPT

• This section cannot be repeated.

• Subsections

  • BFGS
  • CG
  • LBFGS
  • PRINT

• Keywords

  • CONSTRAINT
  • EPS_SYMMETRY
  • EXTERNAL_PRESSURE
  • KEEP_ANGLES
  • KEEP_SPACE_GROUP
  • KEEP_SYMMETRY
  • MAX_DR
  • MAX_FORCE
  • MAX_ITER
  • OPTIMIZER
  • PRESSURE_TOLERANCE
  • RMS_DR
  • RMS_FORCE
  • SPGR_PRINT_ATOMS
  • STEP_START_VAL
  • SYMM_EXCLUDE_RANGE
  • SYMM_REDUCTION
  • TYPE

• Keyword descriptions

  CONSTRAINT
  	CONSTRAINT {Keyword}
  	Imposes a constraint on the pressure tensor by fixing the specified cell components.
  	This keyword cannot be repeated and it expects precisely one keyword.
  	Default value: NONE
  	List of valid keywords: NONE Fix nothing X Fix only x component XY Fix x and y component XZ Fix x and z component Y Fix only y component YZ Fix y and z component Z Fix only z component

  EPS_SYMMETRY
  	EPS_SYMMETRY {Real}
  	Accuracy for space group determination. EPS_SYMMETRY is dimensionless. Roughly speaking, two scaled (fractional) atomic positions v1, v2 are considered identical if |v1 - v2| < EPS_SYMMETRY.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 1.00000000E-004

  EXTERNAL_PRESSURE
  	EXTERNAL_PRESSURE {Real} ...
  	Specifies the external pressure (1 value or the full 9 components of the pressure tensor) applied during the cell optimization.
  	This keyword cannot be repeated and it expects a list of reals.
  	Default value: 1.00000000E+002 0.00000000E+000 0.00000000E+000 0.00000000E+000 1.00000000E+002 0.00000000E+000 0.00000000E+000 0.00000000E+000 1.00000000E+002
  	Default unit: [bar]

  KEEP_ANGLES
  	KEEP_ANGLES {Logical}
  	Keep angles between the cell vectors constant, but allow the lenghts of the cell vectors to change independently. Albeit general, this is most useful for triclinic cells, to enforce higher symmetry, see KEEP_SYMMETRY.
  	This keyword cannot be repeated and it expects precisely one logical.
  	The lone keyword behaves as a switch to .TRUE.
  	Default value: .FALSE.

  KEEP_SPACE_GROUP
  	KEEP_SPACE_GROUP {Logical}
  	Detect space group of the system and preserve it during optimization. The space group symmetry is applied to coordinates, forces, and the stress tensor. It works for supercell. It does not affect/reduce computational cost. Use EPS_SYMMETRY to adjust the detection threshold.
  	This keyword cannot be repeated and it expects precisely one logical.
  	The lone keyword behaves as a switch to .TRUE.
  	Default value: .FALSE.

  KEEP_SYMMETRY
  	KEEP_SYMMETRY {Logical}
  	Keep the requested initial cell symmetry (e.g. during a cell optimisation). The initial symmetry must be specified in the &CELL section.
  	This keyword cannot be repeated and it expects precisely one logical.
  	The lone keyword behaves as a switch to .TRUE.
  	Default value: .FALSE.

  MAX_DR
  	MAX_DR {Real}
  	Convergence criterion for the maximum geometry change between the current and the last optimizer iteration.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 3.00000000E-003
  	Default unit: [bohr]

  MAX_FORCE
  	MAX_FORCE {Real}
  	Convergence criterion for the maximum force component of the current configuration.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 4.50000000E-004
  	Default unit: [bohr^-1*hartree]

  MAX_ITER
  	MAX_ITER {Integer}
  	Specifies the maximum number of geometry optimization steps. One step might imply several force evaluations for the CG and LBFGS optimizers.
  	This keyword cannot be repeated and it expects precisely one integer.
  	Default value: 200

  OPTIMIZER
  	OPTIMIZER {Keyword}
  	Specify which method to use to perform a geometry optimization.
  	This keyword cannot be repeated and it expects precisely one keyword.
  	Default value: BFGS
  	List of valid keywords: BFGS Most efficient minimizer, but only for 'small' systems, as it relies on diagonalization of a full Hessian matrix CG conjugate gradients, robust minimizer (depending on the line search) also OK for large systems LBFGS Limited-memory variant of BFGS suitable for large systems. Not as well fine-tuned but can be more robust.
  	Alias names for this keyword: MINIMIZER
  	This keyword cites the following reference: [BYRD1995]

  PRESSURE_TOLERANCE
  	PRESSURE_TOLERANCE {Real}
  	Specifies the Pressure tolerance (compared to the external pressure) to achieve during the cell optimization.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 1.00000000E+002
  	Default unit: [bar]

  RMS_DR
  	RMS_DR {Real}
  	Convergence criterion for the root mean square (RMS) geometry change between the current and the last optimizer iteration.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 1.50000000E-003
  	Default unit: [bohr]

  RMS_FORCE
  	RMS_FORCE {Real}
  	Convergence criterion for the root mean square (RMS) force of the current configuration.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 3.00000000E-004
  	Default unit: [bohr^-1*hartree]

  SPGR_PRINT_ATOMS
  	SPGR_PRINT_ATOMS {Logical}
  	Print equivalent atoms list for each space group symmetry operation.
  	This keyword cannot be repeated and it expects precisely one logical.
  	The lone keyword behaves as a switch to .TRUE.
  	Default value: .FALSE.

  STEP_START_VAL
  	STEP_START_VAL {Integer}
  	The starting step value for the CELL_OPT module.
  	This keyword cannot be repeated and it expects precisely one integer.
  	Default value: 0

  SYMM_EXCLUDE_RANGE
  	SYMM_EXCLUDE_RANGE {Integer} {Integer}
  	Range of atoms to exclude from space group symmetry. These atoms are excluded from both identification and enforcement. This keyword can be repeated.
  	This keyword can be repeated and it expects precisely 2 integers.

  SYMM_REDUCTION
  	SYMM_REDUCTION {Real} {Real} {Real}
  	Direction of the external static electric field. Some symmetry operations are not compatible with the direction of an electric field. These operations are used when enforcing the space group.
  	This keyword cannot be repeated and it expects precisely 3 reals.
  	Default values: 0.00000000E+000 0.00000000E+000 0.00000000E+000

  TYPE
  	TYPE {Keyword}
  	Specify which kind of method to use for the optimization of the simulation cell
  	This keyword cannot be repeated and it expects precisely one keyword.
  	Default value: DIRECT_CELL_OPT
  	List of valid keywords: DIRECT_CELL_OPT Performs a geometry and cell optimization at the same time. The stress tensor is computed at every step GEO_OPT Performs a geometry optimization (the GEO_OPT section must be defined) between cell optimization steps. The stress tensor is computed at the optimized geometry. MD Performs a molecular dynamics run (the MD section needs must defined) for computing the stress tensor used for the cell optimization.