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 and can be optional.

• Subsections

  • BFGS
  • CG
  • LBFGS
  • PRINT

• Keywords

  • EXTERNAL_PRESSURE
  • KEEP_ANGLES
  • KEEP_SYMMETRY
  • MAX_DR
  • MAX_FORCE
  • MAX_ITER
  • OPTIMIZER
  • PRESSURE_TOLERANCE
  • RMS_DR
  • RMS_FORCE
  • STEP_START_VAL
  • TYPE

• Keyword descriptions

  EXTERNAL_PRESSURE
  	EXTERNAL_PRESSURE {REAL} .. {REAL}
  	Specifies the external pressure (1 value or the full 9 components of the pressure tensor) applied during the cell optimization.
  	This optional keyword cannot be repeated and it expects a list of reals.
  	Default value: 1.00000000E+02 0.00000000E+00 0.00000000E+00 0.00000000E+00 1.00000000E+02 0.00000000E+00 0.00000000E+00 0.00000000E+00 1.00000000E+02
  	Default unit: [bar]

  KEEP_ANGLES
  	KEEP_ANGLES TRUE
  	Keep angles between the cell vectors constant, but allow the lenghts of the cell vectors to change independently. For example, a cubic cell might become orthorhombic, but not triclinic.
  	This optional 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 YES
  	Keep the requested initial cell symmetry (e.g. during a cell optimisation). See cell section for how to impose a cell symmetry.
  	This optional 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 criterium for the maximum geometry change between the current and the last optimizer iteration.
  	This optional keyword cannot be repeated and it expects precisely one real.
  	Default value: 3.00000000E-03
  	Default unit: [bohr]

  MAX_FORCE
  	MAX_FORCE {REAL}
  	Convergence criterium for the maximum force component of the current configuration.
  	This optional keyword cannot be repeated and it expects precisely one real.
  	Default value: 4.50000000E-04
  	Default unit: [bohr^-1hartree]

  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 optional keyword cannot be repeated and it expects precisely one integer.
  	Default value: 200

  OPTIMIZER
  	OPTIMIZER {BFGS|LBFGS|CG}
  	Specify which method to use to perform a geometry optimization.
  	This optional 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 Limit memory variant of the above, can also be applied to large systems, not as well fine-tuned
  	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 optional keyword cannot be repeated and it expects precisely one real.
  	Default value: 1.00000000E+02
  	Default unit: [bar]

  RMS_DR
  	RMS_DR {REAL}
  	Convergence criterium for the root mean square (RMS) geometry change between the current and the last optimizer iteration.
  	This optional keyword cannot be repeated and it expects precisely one real.
  	Default value: 1.50000000E-03
  	Default unit: [bohr]

  RMS_FORCE
  	RMS_FORCE {REAL}
  	Convergence criterium for the root mean square (RMS) force of the current configuration.
  	This optional keyword cannot be repeated and it expects precisely one real.
  	Default value: 3.00000000E-04
  	Default unit: [bohr^-1hartree]

  STEP_START_VAL
  	STEP_START_VAL <INTEGER>
  	The starting step value for the CELL_OPT module.
  	This optional keyword cannot be repeated and it expects precisely one integer.
  	Default value: 0

  TYPE
  	TYPE (GEO_OPT|MD|DIRECT_CELL_OPT)
  	Specify which kind of method to use for the optimization of the simulation cell
  	This optional 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.