Building and Optimizing Diborane B2H6.

To "build" diborane load "BH3" twice from the library. To load the second BH3 use ADD.Mol on the build menu. This will give

Run Mopac using defaults and the optimized structure should be

For cosmetic purposes you can add the two "missing" lines using the Mk.CONN function on the build menu. Use Mk.CONN twice each time select the H atom first.

How good is the result ?
Use the button in build mode to measure the bond lengths and angles and you should get the following.
B-Hter 1.191 (Obs. 1.192)
B-Hbr 1.331 (Obs. 1.329)
Hter-B-Hter 124.8 (Obs121.8)
Hbr-B-Hbr 97.2 (Obs 96.5)
The agreement between AM1 calaculations and experimental data is quite good.