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cubeprop() Generation of cube files

Code author: Robert M. Parrish and Francesco A. Evangelista

Section author: Francesco A. Evangelista


Evaluate properties on a grid and generate cube files.

New in version 0.5: wfn parameter passed explicitly

Parameters:wfn (Wavefunction) – set of molecule, basis, orbitals from which to generate cube files
>>> # [1] Cube files for all orbitals
>>> E, wfn = energy('b3lyp', return_wfn=True)
>>> cubeprop(wfn)
>>> # [2] Cube files for density (alpha, beta, total, spin) and four orbitals 
>>> #     (two alpha, two beta)
>>> set cubeprop_tasks ['orbitals', 'density']
>>> set cubeprop_orbitals [5, 6, -5, -6]
>>> E, wfn = energy('scf', return_wfn=True)
>>> cubeprop(wfn)


Psi4 has the ability to export cube files that store information about basis functions, molecular orbitals, the electron density, and the electrostatic potential (ESP). Cube files store the value of a scalar quantity on a regular Cartesian grid, and can be visualized with several visualization programs, some of which are free, like VMD (

An example utilization of the code is:

molecule h2o {
0 1
H 1 1.0
H 1 1.0 2 104.5

set basis cc-pvdz
set scf_type df
set freeze_core True
set cubeprop_tasks ['orbitals']
set cubeprop_orbitals [5,6,-5,-6]

E, wfn = energy('scf', return_wfn=True)

In this example, the cubeprop() call after the energy('scf') command executes the cubeprop code. The array CUBEPROP_TASKS specifies which tasks should be executed. In this case the task 'orbitals' generates cube files for orbitals. The CUBEPROP_ORBITALS option specifies that cube files should be generated only for alpha orbitals 5 (HOMO) and 6 (LUMO) and beta orbitals 5 (indicated as -5) and 6. If the option CUBEPROP_ORBITALS is not provided, then cube files are generated for all orbitals. After running, the above input will generate four files: Psi_a_5.cube, Psi_a_6.cube, Psi_b_5.cube, and Psi_b_6.cube.


If your cube plots are too coarse, try to decrease the grid spacing via the option CUBIC_GRID_SPACING. If the edges of your plot are cut then increase the size of the grid via the option CUBIC_GRID_OVERAGE.

Cubeprop Tasks

The cubeprop utility can be provided a list of tasks to perform. Tasks are specified by the CUBEPROP_TASKS option, which is a list of strings that identify the tasks. Several tasks are available. These include:

ORBITALS [Default if CUBEPROP_TASKS is not specified]
Produces cube representations of the molecular orbitals \psi_q(\mathbf{r}). Orbitals are sorted according to increasing orbital energy ignoring symmetry.
This task can be used to obtain the alpha and beta electron densities, \rho_\alpha(\mathbf{r}) and \rho_\beta(\mathbf{r}), together with the total density \rho(\mathbf{r}) = \rho_\alpha(\mathbf{r}) + \rho_\beta(\mathbf{r}), and the spin density \rho(\mathbf{r}) = \rho_\alpha(\mathbf{r}) - \rho_\beta(\mathbf{r}).
This task is useful to produce cube files of the atomic orbital basis functions \chi_\mu(\mathbf{r}).
Calculates the total (nuclear + electronic) electrostatic potential V(\mathbf{r}).


The ESP task requires the user to specify a density-fitting basis via the DF_BASIS_SCF keyword.


It is important to specify the CUBEPROP_ORBITALS option when dealing with large molecules to avoid running out of disk space. For example, using the default grid spacing of 0.2 Ångström, the size of a single cube file for a molecule like water is of the order of 1.4 MB. For a molecule with 200 basis functions, the cube files for all the orbitals occupy more than half a GB.



Properties to compute. Valid tasks include: DENSITY - Da, Db, Dt, Ds ESP - Dt, ESP ORBITALS - Psi_a_N, Psi_b_N BASIS_FUNCTIONS - Phi_N LOL - LOLa, LOLb ELF - ELFa, ELFb

  • Type: array
  • Default: No Default


Directory to which to write cube files. Default is the input file directory.

  • Type: string
  • Default: No Default


List of orbital indices for which cube files are generated (1-based, + for alpha, - for beta). All orbitals computed if empty.

  • Type: array
  • Default: No Default


List of basis function indices for which cube files are generated (1-based). All basis functions computed if empty.

  • Type: array
  • Default: No Default


CubicScalarGrid grid spacing in bohr [D_X, D_Y, D_Z]. Defaults to 0.2 bohr each.

  • Type: array
  • Default: No Default


CubicScalarGrid spatial extent in bohr [O_X, O_Y, O_Z]. Defaults to 4.0 bohr each.

  • Type: array
  • Default: No Default

Orbital Visualization with VMD

Included in Psi4 is functionality to automatically render specified surfaces, including molecular orbitals, densities, and basis functions, using VMD. The script takes the .cube files generated in a calculation and generates images alinged with user-input specifications. The script is located in psi4//share/scripts/

Script Prerequisites

  1. VMD must be installed, and it can be downloaded for free at ( Additionally, the script needs to know where to find the VMD executable, and this is defined as VMDPATH. VMDPATH must be defined as an environment variable.
  2. To generate images with multiple surfaces, ImageMagick must also be installed. ImageMagick is a free program which can be installed using homebrew/pip or from .
  3. With ImageMagick installed, an environment variable called MONTAGE needs to be created which points to the montage executable. This executable can be found in the /bin/ sub-directory wherever ImageMagick was installed.

Running the Script

  1. Run a Psi4 calculation, generating .cube files as detailed in the above documentation.

  2. Copy into a directory where the image files are desired, and pass the directory pointing to the .cube files as an argument to run:

    python /path/to/cube/files/

    Alternatively, the script can be run in the same directory as the cube files with no need to pass the directory as an argument.

  3. For an additional image containing all surfaces in an array (very useful for hand-picking orbital spaces), set the montage flag to True:

    python /path/to/cube/files/ --montage=True
  1. As an example, take the cube files generated from the water calculation from the above input file. Using the script and montage, the alpha molecular orbitals, for example, can be rendered and output in one image with:

    python /path/to/cube/files/ --montage=True --opacity=0.5 --rx=90 --ry=60

The desired image in this case is called “AlphaMOs.tga”, and looks like this:

Alpha MOs

Script Options

>>> ./ --help
usage: [-h] [--color1 [<integer>]] [--color2 [<integer>]]
                   [--iso [<isovalue>]] [--rx [<angle>]] [--ry [<angle>]]
                   [--rz [<angle>]] [--tx [<angle>]] [--ty [<angle>]]
                   [--tz [<angle>]] [--opacity [<opacity>]]
                   [--scale [<factor>]] [--montage [MONTAGE]]
                   [--imagesize [<integer>]] [--fontsize [<integer>]]
                   [<cubefile dir>]
vmd_cube is a script to render cube files with vmd. To generate cube files
with Psi4, add the command cubeprop(wfn) at the end of your input file, where
*wfn* is a Wavefunction object that may be retrieved from any calculation and
used following the pattern "ene, wave = energy('pbe', return_wfn=True)\n
positional arguments:
  <cubefile dir>        The directory containing the cube files.
optional arguments:
  -h, --help            show this help message and exit
  --color1 [<integer>]  the color ID of surface 1 (integer, default = 3)
  --color2 [<integer>]  the color ID of surface 2 (integer, default = 23)
  --iso [<isovalue>]    the isosurface value (float, default = 0.05)
  --rx [<angle>]        the x-axis rotation angle (float, default = 30.0)
  --ry [<angle>]        the y-axis rotation angle (float, default = 40.0)
  --rz [<angle>]        the z-axis rotation angle (float, default = 15.0)
  --tx [<angle>]        the x-axis translation (float, default = 0.0)
  --ty [<angle>]        the y-axis translation (float, default = 0.0)
  --tz [<angle>]        the z-axis translation (float, default = 0.0)
  --opacity [<opacity>]
                        opacity of the isosurface (float, default = 1.0)
  --scale [<factor>]    the scaling factor (float, default = 1.0)
  --montage [MONTAGE]   call montage to combine images. (string, default =
  --imagesize [<integer>]
                        the size of each image (integer, default = 250)
  --fontsize [<integer>]
                        the font size (integer, default = 20)