cellParameter

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Purpose

The cellParameter command is a TCL function to get and set the cell parameters of a periodic molecular system.

Syntax

Getting cell parameters:

cellParameter

Setting cell parameters:

cellParameter ?-option? a b c alpha beta gamma



Keyword      Values           Default           Meaning

-option      -atomAffine      -atomAffine   The fractional coordinates of all 
                                            atoms in the cell are unchanged.

             -moleculeAffine                The fractional coordinates of the 
                                            center of mass of each molecule in 
                                            the cell are unchanged.

             -noAffine                      The Cartesian coordinates of all 
                                            atoms before and after the cell 
                                            distortion remain the same.

a            real                           The length in angstroms of the
                                            a coordinate of the cell.

b            real                           The length in angstroms of the
                                            b coordinate of the cell.

c            real                           The length in angstroms of the
                                            c coordinate of the cell.

alpha        real                           The angle between the b and c
                                            axes of the cell.

beta         real                           The angle between the a and c
                                            axes of the cell.

gamma        real                           The angle between the a and b
                                            axes of the cell.

Description

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The cellParameter keyword, used alone, gets the cell parameters. That is, it returns a TCL list (using the current tcl_precision) of the a, b, c, alpha, beta, gamma parameters.

If you supply the a, b, c, alpha, beta, gamma parameters in the command line, the cellParameter command sets the system parameters to the values supplied. Note: if fewer than 6 parameters are given, then the existing (default, or previously set) values are used for the remaining parameters. If more than 6 parameters are supplied, an error is generated. The optional -option values and their effects are listed in the above table.

Example 1

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cellParameter

This example of the cellParameter command returns the present values of the cell parameters: the a, b, and c lengths and the alpha, beta, and gamma angles.

Example 2

cellParameter 5.0 5.0 5.0

This example of the cellParameter command sets the a, b, and c lengths to 5 Å without changing the values of the cell angles.

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