## 6.5 The Energy Level Diagram Window

Choosing `Energy level diagram` from the main window menu will result in a new window showing the calculated MO energies in an energy level diagram. In this window the mouse acts as follows:

- Clicking with the left mouse button on a line
  A box appears containing the symmetry and the energy for this MO. Selecting a MO can also be achieved by pressing the cursor keys for moving up and down , respectively.
- Clicking in the window, pressing the middle mouse button and holding it down
  With the rubber band box drawn one can zoom into the diagram.
- Pressing the right mouse button
  A menu will appear.

  Figure 11: The dialog box for setting the energy units for the MO energy level diagram

  The menu contains the following topics:
  - Settings for energy level diagram ... (Alt+S)
    Selecting this topic displays the dialog shown in the Figure.
    - Units
      The four buttons can be used to select the energy unit. Available are Hartrees (default), kJ/mol, eV, and cm-1.
    - Resolution for density of states
      This slider can be used to change the resolution for the density of states. A smaller value results in a higher resolution. The default is 0.01. The minimum, maximum, and default values can be set in the resource file. (vide infra, p. ).
  - Select molecule
    Provides a submenu with the names of all molecules currently loaded and can be used to change the molecule for the currently displayed energy level diagram. Another possibility to select a molecule consists of pressing the `Tab` key, which cycles through all entries in the `Select molecule` submenu.
  - Transition (Alt+T)
    This topic can be used to calculate the energy for a transition between two MO's. This topic is available only if one MO was selected by clicking on it. Choosing this menu topic followed by clicking on an other MO draws a line showing the transition and a box containing the symmetry labels and the energy difference between these two MO's. Further clicks on other MO's repeat calculations of energy differences. To leave this mode click either somewhere in the window were no MO's are or select this topic from the menu again.
  - Zoom out (Alt+Z)
    This topic can be used to zoom out of the diagram after previous zoom-ins. The zoom mechanism stores all previous enlargement steps. By selecting this topic you move back one step.
  - Save drawing (Alt+D)
    The same dialog box as for `Save drawing` in the main menu is shown and allows you to save the energy level diagram as a TIFF, PNG, HPGL, or PostScript file (cf. p. ).
  - Draw density of states (Alt+D)
    This topic can be used to toggle between the density of states and the energy level diagram. The energy level diagram is the default.
  - Foreground color (Alt+F)
    The foreground color of the diagram can be changed using the color editor (vide infra, p. ).
  - Background color (Alt+B)
    The background color of the diagram can be changed using the color editor (vide infra, p. ).
  - Quit energy diagram (Q)
    This closes the energy level diagram window.