Hartree-Fock calculations using Spartan'06 will attempt to
use a very fast procedure in which all integrals are kept in memory. The
maximum size of molecule permitted is dictated by available memory according
to the following (closed-shell case):
(number of basis functions)4 < available
where available memory = (unused memory) - 48 MB
This translates into approximately 160 basis functions for
a single-processor machine with 1 GB of installed memory.
This limit is automatically enforced. However, Spartan'06 cannot predict
the future memory usage of other Spartan jobs, the operating system or
other applications. To avoid problems and at the same time take maximum
advantage of the fast Hartree-Fock methods, run only one job at a time,
or enforce a memory limit via the Limits menu found in the job
The fast Hartree-Fock methods will not be used under any conditions if the
keyword FASTHF=OFF is entered into the Options box
in the Calculations dialog.