Gaussian and disk space

When you run out of disk space in Gaussian, it may not be because you have reached the limits of the computer. Make sure you take full advantage of the computer's memory by specifying %mem. The integral calculation is done through a combination of memory and disk operations, so maximizing both is important. Memory is especially important as it is faster than disk operations by many orders of magnitude. Having said this, disk space is crucial and you can be having two possible problems:

• You need a larger MaxDisk!!! (most common) Solutions:
  • Increase MaxDisk to 1900 MB in Linux or to 50% of available space on a 64-bit supercomputer:
    # MaxDisk=1900MB RHF/6-31G* Opt
  • On Linux, you cannot have file sizes over 2 GB, but Gaussian allows you to have multiple scratch areas by doing the following:

    %rwf=/scratch-dir/w1.rwf, 1900MB, /scratch-dir/w2.rwf, 1900MB, /scratch-dir/w3.rwf,1900MB, /scratch-dir/w4.rwf,1900MB, /scratch-dir/w5.rwf, 1900MB...

    (you could go further depending on the number of characters but keep it on one line)

    %mem=...

    # MaxDisk=9500MB ...

• The other problem is that you have exceeded what is possible in the scratch directory on that computer currently or what would be possible at all. To find out what is possible on that computer, you can run the command 'df -k' which will give the disk size and current usage in kilobytes. If you need more, try a different computer or ask the system administrator if there are old files that can be cleaned out.

Where are the scratch directories?

On our cluster, replace /scratch-dir with /scr.