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.

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 replicas 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

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.

x1: DISTANCE ATOMS=1,2
x2: DISTANCE ATOMS=1,3
x3: ANGLE ATOMS=1,2,3

hA1: HISTOGRAM ARG=x1,x2,x3 GRID_MIN=0.0,0.0,0.0 GRID_MAX=3.0,3.0,3.0 GRID_BIN=10,10,10 BANDWIDTH=1.0,1.0,1.0
DUMPCUBE GRID=hA1 FILE=histoA1.cube