Talk:Mod:inorganic

A few common problems

In the frequency calculation for BH3, some people have found that the symmetry of the molecule has changed from D3h to C3h. If you open your (text) input file, you will see that the three B-H bond lengths are slightly different. Any differences smaller than the first three decimal places are not significant to the structure of the molecule but may cause problems in the calculation. You should therefore delete the final decimal places leaving all three bond lengths the same and use this file to restart your calculation. You can also set the point group to D3h (in Edit/Point group) so it cannot change during the calculation.

For the bigger jobs some people have had error messages opening their output files in Gaussview. If you open the text file and scroll down to the bottom you can identify the error. A 9999 error means that the maximum number of steps has been exceeded for some parameter (normally the number of optimisation steps) without the job converging. Open the log file making sure you tick the load all geometries option. Then look at "Optimisation" in the "Results" tab of gaussview. If the graph showing the energy vs steps in the optimisation appears to be almost a straight line, and the gradient graph (below the E vs step graph) appears to have reached zero, it is possible that a minimum has been found but Gaussian has had trouble recognising this so has continued to calculate more steps. You can check this by looking a little further up in your output file where it will tell you if the force (that is, the gradient) has converged (search for the "Item" section). To solve this problem you should restart the calculation from the final geometry of the job but tick the box "use tight convergence criteria".

After an interesting series of errors, all have finally been resolved, and we can get MOPAC2007 finally running. The advantage of doing so is that calculations for e.g. Au, using the PM6 method, can be run in literally just a few seconds. Thus Au₂Na₂ can be investigated in < 30 seconds. Mo(CO)4L2 where L=P(CH3)3 takes around 10 seconds to optimize. It would be interesting if someone could compare the results of PM6 with the DFT calculations (which take rather longer). Bring your laptop to me if you want MOPAC2007 activated/fixed.--Rzepa 16:20, 29 October 2008 (UTC)