The freqmem utility takes parameters for a frequency calculation and determines the amount of memory required to complete all steps in one pass, for maximum efficiency. All parameters must be provided on the command line, using the following syntax:
freqmem natoms nbasis r|u c|d functions
where the arguments are:
natoms
Number of atoms in the molecule.
nbasis
Number of basis functions for this system under the desired basis set.
r|u
A one-letter code indicating an RHF (closed shell) or UHF (open shell) calculation, as appropriate.
c|d
A one-letter code indicating whether the calculation will be run using the conventional or direct algorithm.
functions
A string indicating the types of basis functions used in the chosen basis set: sp, spd, spdf, and so on.
Here is an example of its use, estimating the memory resources required for RHF/STO-3G frequencies on taxol (113 atoms):
$ freqmem 113 361 r d sp RHF direct frequencies with sp functions: One pass requires 44.80 megawords.
The output indicates that the program will require about 360 MB of memory to complete the frequency calculation in a single pass.
If the amount of memory specified by freqmem is not available, a frequency calculation can still be completed using multiple passes. Use the %Mem Link 0 command to specify the amount of available memory. Setting this parameter to one half or one third of the amount of memory recommended by freqmem is often a good choice.
The number of basis functions used in a Gaussian calculation is printed out early in the output file. It may also be calculated by setting up an input file for the job in question, and including the %KJob=301 Link 0 command, which tells the program to terminate as soon as Link 301 is reached (which is almost immediately). The number of basis functions used for the molecule with the specified basis set may then be retrieved from the log file with a command like this one:
$ grep "basis func" name.log
361 basis functions 1083 primitive gaussians
Last updated on: 9 Jun 2009