FINDIF: Finite Differences

A graphical tool for analyzing one-dimensional potentials

FINDIF is a Windows-based application for calculating the eigenstates and corresponding eigenvalues of one-dimensional potentials. Periodic and non-periodic potentials can be analyzed, and either the amplitude or the square amplitude of the eigenstate can be displayed.

On the right is a screenshot of the FINDIF interface, showing the analysis of the double-well potential of ammonia. The potential (in wavenumbers) is shown in red, and the wavefunction for the ground vibrational state is shown in white. The dashed white line represents the energy of the state. Click here for a higher resolution image of the screenshot.

  • Installing FINDIF
  • Using FINDIF
  • Contact information
    • Installing FINDIF: FINDIF is available free-of-charge.
     
  • Download the file FINDIF-Installer.zip and save it in a temporary folder on your computer.
  • Double-click the zip file to open it, then double-click the setup executable. Installation will begin. We suggest installing FINDIF in C:\Program Files\FINDIF, but any folder will work.
  • Run FINDIF by double-clicking the FINDIF executable in your FINDIF folder. A sample potential for (non-periodic) ammonia inversion is available in the installation zip file.
  • FINDIF is now installed on your computer. You can delete the zip file.
    • Using FINDIF: The following virtual controls are available to the user.
     
  • Vibrational Eigenstate: This control allows the user to select the displayed eigenstate. The eigenvalue of the state is given in wavenumbers. For the ammonia potential that appears in the screenshot, the ground vibrational state (v=0) has an energy of 531.785 cm-1, relative to the minimum of the potential.
  • Reduced Mass: The reduced mass (in amu) is set using a virtual dial. When using potentials from intrinsic reaction coordinate calculations, this mass should be set to one, as shown.
  • y Scale: This dial allows the user to scale the amplitude of the eigenstate relative to the potential.
  • y/ y2: This switch allows the user to examine either the amplitude or the square amplitude of the eigenstate.
  • Non-periodic/Periodic: Set this switch to the appropriate position for the potential being analyzed. Note that, for example, analyzing the periodic torsional potential of ethane with this switch set to Non-periodic will yield bogus results.
  • Read Potential: Clicking this button opens a dialog box asking the user to identify a text file that specifies the potential. The potential, V(x), should be given as a series of x,V points, arranged in two columns. The x values must be equally spaced, in either Å or Å amu-1/2 units (the latter for IRC potentials). The V values must be given in cm-1 units. Click here to view the file used to make the screenshot.
  • Save Eigenstate: Clicking this button opens a dialog box asking the used to specify an external text file to which the eigenstate will be exported. This is useful for making images of eigenstates various plotting packages, including Microsoft Excel.
  • Quit: Clicking this button exits the application.
    • FINDIF is a LabVIEW virtual instrument (National Instruments). The FINDIF interface was developed by Eric D. Glendening based on a Fortran finite difference code written by Arthur M. Halpern.
    Department of Chemistry and Physics, Indiana State University, Terre Haute, IN  47809
    Comments to glendening@indstate.edu
    Last updated:  June 18, 2012