This is part of the gridtools module

Output a three dimensional grid using the Gaussian cube file format.

Suppose you have calculated the value of a function on a three dimensional grid. This function might be a HISTOGRAM or it might be a free energy energy surface that was calculated from this histogram by using CONVERT_TO_FES. Alternatively, your function might be a phase-field that was calculated using MULTICOLVARDENS. Whatever the function is, however, you obviously cannot show it using a typical contour plotting program such as gnuplot as you have three input variables.

Tools like VMD have nice features for plotting these types of three dimensional functions but typically you are required to use a Gaussian cube file format to input the data. This action thus allows you to output a function evaluated on a grid to a Gaussian cube file format.

Examples

The input below can be used to post process a trajectory. A histogram as a function of the distance between atoms 1 and 2, the distance between atom 1 and 3 and the angle between the vector connecting atoms 1 and 2 and 1 and 3 is computed using kernel density estimation. Once all the data contained in the trajectory has been read in and all the kernels have been added the resulting histogram is output to a file called histoA1.cube. This file has the Gaussian cube file format. The histogram can thus be visualized using tools such as VMD.

Click on the labels of the actions for more information on what each action computes

x1: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2 The DISTANCE action with label x1 calculates a single scalar value
x2: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,3 The DISTANCE action with label x2 calculates a single scalar value
x3: ANGLE ATOMSthe list of atoms involved in this collective variable (either 3 or 4 atoms). =1,2,3 The ANGLE action with label x3 calculates a single scalar value
hA1: HISTOGRAM ARGthe input for this action is the scalar output from one or more other actions. =x1,x2,x3 GRID_MINcompulsory keyword 
the lower bounds for the grid =0.0,0.0,0.0 GRID_MAXcompulsory keyword 
the upper bounds for the grid =3.0,3.0,3.0 GRID_BINthe number of bins for the grid =10,10,10 BANDWIDTHcompulsory keyword 
the bandwidths for kernel density estimation =1.0,1.0,1.0 The HISTOGRAM action with label hA1
DUMPCUBE GRIDcompulsory keyword 
the action that creates the grid you would like to output =hA1 FILEcompulsory keyword ( default=density )
the file on which to write the grid. =histoA1.cube The DUMPCUBE action with label

Glossary of keywords and components

Compulsory keywords

GRID	the action that creates the grid you would like to output
STRIDE	( default=0 ) the frequency with which the grid should be output to the file. The default value of 0 ensures that the grid is only output at the end of the trajectory
FILE	( default=density ) the file on which to write the grid.
REPLICA	( default=0 ) the replica for which you would like to output this information

Options

FMT	the format that should be used to output real numbers
COMPONENT	if your input is a vector field use this to specify the component of the input vector field for which you wish to output