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## Section CELL

• Input parameters needed to set up the simulation cell. Simple products and fractions combined with functions of a single number can be used like 2/3, 0.3*COS(60) or -SQRT(3)/2. The functions COS, EXP, LOG, LOG10, SIN, SQRT, and TAN are available.
• Section path: ```CP2K_INPUT / FORCE_EVAL / QMMM / CELL```
• This section cannot be repeated.

• ### Keyword descriptions

 `A`` {Real}`` {Real}`` {Real}` Specify the Cartesian components for the cell vector A. This defines the first column of the h matrix. This keyword cannot be repeated and it expects precisely 3 reals. Default unit:``` [angstrom] ```
 `ABC`` {Real}`` {Real}`` {Real}` Specify the lengths of the cell vectors A, B, and C, which defines the diagonal elements of h matrix for an orthorhombic cell. For non-orthorhombic cells it is possible either to specify the angles ALPHA, BETA, GAMMA via ALPHA_BETA_GAMMA keyword or alternatively use the keywords A, B, and C. The convention is that A lies along the X-axis, B is in the XY plane. This keyword cannot be repeated and it expects precisely 3 reals. Default unit:``` [angstrom] ```
 `ALPHA_BETA_GAMMA`` {Real}`` {Real}`` {Real}` Specify the angles between the vectors A, B and C when using the ABC keyword. The convention is that A lies along the X-axis, B is in the XY plane. ALPHA is the angle between B and C, BETA is the angle between A and C and GAMMA the angle between A and B. This keyword cannot be repeated and it expects precisely 3 reals. Default values: `9.00000000E+001 9.00000000E+001 9.00000000E+001` Default unit:``` [deg] ``` Alias names for this keyword: ANGLES
 `B`` {Real}`` {Real}`` {Real}` Specify the Cartesian components for the cell vector B. This defines the second column of the h matrix. This keyword cannot be repeated and it expects precisely 3 reals. Default unit:``` [angstrom] ```
 `C`` {Real}`` {Real}`` {Real}` Specify the Cartesian components for the cell vector C. This defines the third column of the h matrix. This keyword cannot be repeated and it expects precisely 3 reals. Default unit:``` [angstrom] ```
 `CELL_FILE_FORMAT`` {Keyword}` Specify the format of the cell file (if used) This keyword cannot be repeated and it expects precisely one keyword. Default value: `CP2K` List of valid keywords: `CIF` Cell info from CIF file. `CP2K` Cell info in the CP2K native format. `XSC` Cell info in the XSC format (NAMD)
 `CELL_FILE_NAME`` {String}` Possibility to read the cell from an external file This keyword cannot be repeated and it expects precisely one string.
 `MULTIPLE_UNIT_CELL`` {Integer}`` {Integer}`` {Integer}` Specifies the numbers of repetition in space (X, Y, Z) of the defined cell, assuming it as a unit cell. This keyword affects only the CELL specification. The same keyword in SUBSYS%TOPOLOGY%MULTIPLE_UNIT_CELL should be modified in order to affect the coordinates specification. This keyword cannot be repeated and it expects precisely 3 integers. Default values: `1 1 1`
 `PERIODIC`` {Keyword}` Specify the directions for which periodic boundary conditions (PBC) will be applied. Important notice: This applies to the generation of the pair lists as well as to the application of the PBCs to positions. See the POISSON section to specify the periodicity used for the electrostatics. Typically the settings should be the same. This keyword cannot be repeated and it expects precisely one keyword. Default value: `NONE` List of valid keywords: `NONE` Without description, yet. `X` Without description, yet. `XY` Without description, yet. `XYZ` Without description, yet. `XZ` Without description, yet. `Y` Without description, yet. `YZ` Without description, yet. `Z` Without description, yet.
 `SYMMETRY`` {Keyword}` Imposes an initial cell symmetry. This keyword cannot be repeated and it expects precisely one keyword. Default value: `NONE` List of valid keywords: `CUBIC` Cubic (a = b = c, α = β = γ = 90°) `HEXAGONAL` Hexagonal (alias for HEXAGONAL_GAMMA_60) `HEXAGONAL_GAMMA_120` Hexagonal (a = b ≠ c, α = β = 90°, γ = 120°) `HEXAGONAL_GAMMA_60` Hexagonal (a = b ≠ c, α = β = 90°, γ = 60°) `MONOCLINIC` Monoclinic (a ≠ b ≠ c, α = γ = 90°, β ≠ 90°) `MONOCLINIC_GAMMA_AB` Monoclinic (a = b ≠ c, α = β = 90°, γ ≠ 90°) `NONE` No cell symmetry `ORTHORHOMBIC` Orthorhombic (a ≠ b ≠ c, α = β = γ = 90°) `RHOMBOHEDRAL` Rhombohedral (a = b = c, α = β = γ ≠ 90°) `TETRAGONAL` Tetragonal (alias for TETRAGONAL_AB) `TETRAGONAL_AB` Tetragonal (a = b ≠ c, α = β = γ = 90°) `TETRAGONAL_AC` Tetragonal (a = c ≠ b, α = β = γ = 90°) `TETRAGONAL_BC` Tetragonal (a ≠ b = c, α = β = γ = 90°) `TRICLINIC` Triclinic (a ≠ b ≠ c ≠ a, α ≠ β ≠ γ ≠ α ≠ 90°)

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