Speeding up Calculations

If a calculation seems to be taking a long time, consider adjusting the following settings. Note that some of these can result in misleading calculations under the "wrong" circumstances.

Make sure PrintLevel is Minimal or None and ShowEstUnc is off. Leaving either of these on can produce a lot of output in the (possibly hidden) log window which is time consuming to calculate and print.
Turning AutoReplot off will stop automatic recalculation of the spectrum; an explicit press of the simulate button is then required for a calculation.
Is the range of J calculated more than required? Consider:

Reducing the range of J values calculated - see Determining J ranges
Reducing the range of J used in calculating the partition function; turn AutoQConverge off.
Not calculating the partition function at all - set IntensityUnits to Arbitrary.

The NoLineList setting will disable the use of saved line lists for simulation; turning this on will use less memory, but at the expense of more calculation when a spectrum is simulated.
If the program runs out of memory, consider the 64 bit version.
If calculating hyperfine structure,setting MaxDJ for Linear, Symmetric or Asymmetric Top nuclei to zero can give significantly faster calculations but may be less accurate, particularly for low J or large hyperfine structure.
Adjusting the number of threads used for the calculation ("View", "Threads") may help for some calculations. Use the operating system task manager or system monitor to see how effective the parallel calculation is; ideally all the CPU's should be operating at 100%, but some calculations may benefit from a smaller number of threads, or only a single thread. "View", "Timing" will give an indication as to where the time is being spent; if it is in matrix diagonalization then the only way to speed the calculation is reducing the size of the problem.