Calculating Energy v.s. Distance Curves for F₂ and "He₂"

The bond scanning function provided in the Iconc options makes this straightforward and the results are plotted using EXCEL.

Build F₂ and measure the F-F bond length using the button and stop this function using . If you do not know how to do this look at the tutorial on Building and Optimizing BF₃.
Return to display mode and you should have.

In build mode click MarkBond on the menu and then click the Geom. button and select the two atoms as if you were calculating the bond length. Click and the marked bond should be blue if the default coulor map is in use..
Go back to display mode and click to bring up the Iconc menu.
Select NewInput and on dialog 15



select B-Scan and check that Steps is set to 60 and click Run Iconc. When the bond scan is complete the following picture should appear.

This curve shows that the minimum energy is at the normal F-F bond distance (1.43 Å).
Curves of this type can be produced by the Morse Function ( E(r) = De(1 - e^(-a(r-re))^2  P.M. Morse 1929) hence the term Morse Curve.

The minimum distance and energy are given in the plot title and the results are lso listed to the GEO file. .

If you repeat this with two He atoms the result should be



There is clearly no bond here.

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