By default, the normal MOPAC output is suppressed. When LARGE is present, the normal MOPAC output is sent to the PARAM file <text>.arc. This output is useful in finding errors in the data sets. For example, if the heat of formation or the gradient on the first cycle of geometry optimization is very large, there is a possibility that the geometry is faulty. Also, if, in a system that is electronically simple, difficulties are reported in the SCF calculation, then the possibility of a faulty electronic state should be considered. This is particularly important in complicated organometallic systems such as heme.
For more diagnostics when using LARGE, add ordinary MOPAC keywords such as PL to the individual data set that's causing problems.