Gaussian 03 Online Manual
The MaxDisk keyword specifies the amount of disk storage available for scratch data, in 8-byte words. The value may optionally be followed by a units designation: KB, MB, GB, KW, MW or GB. Normally, this is set for a site in the site-wide Default.Route file.
MP3, MP4, QCISD, CCSD, QCISD(T), and CCSD(T) calculations all now look at MaxDisk. If the calculation can be done using a full integral transformation while keeping disk usage under MaxDisk, this is done; if not, a partial transformation is done and some terms are computed in the AO basis. Since MP2 obeys MaxDisk as much as possible, the Stingy, NoStingy and VeryStingy options are not needed.
Thus, it is crucial for a value for MaxDisk to be specified explicitly for these types of jobs, either within the route section or via a system wide setting in the Default.Route file. If MaxDisk is left unset, the program now assumes that disk is abundant and performs a full transformation by default (in contrast to Gaussian 94 where a partial transformation was the default in such cases). If MaxDisk is not set and sufficient disk space is not available for a full transformation, the job will fail.
Not all calculations can dynamically control their disk usage, so the effects of this keyword vary:
Click here for a detailed discussion of the efficient use of disk resources in Gaussian calculations.