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 function
The arguments are:
Number of atoms in the molecule.
Number of basis functions for this system under the desired basis set.
A one-letter code indicating an RHF (closed shell) or UHF (open shell) calculation, as appropriate.
A letter indicating the highest angular momentum basis function in the basis set: i.e., d for d functions, f for f functions, h for h functions, and so on. This parameter may also be a string indicating the types of basis functions used in the chosen basis set: sp, spd or spdf (as was used in earlier versions of this utility).
This examples estimates the memory resources required for RHF/STO-3G frequencies on taxol (113 atoms):
$ freqmem 113 361 r p 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: 23 July 2019. [G16 Rev. C.01]