13.1 Memory control

MOLPRO stores all internal data in a single big working area, which is allocated dynamically in the beginning of the calculation. The default amount of memory, as specified with the -m option in the molpro.rc file, is 8 MW (64 Mb). For big calculations more memory may be needed, and the default can then be modified using the memory directive. This should be the first command in the input (after the *** title card, if present, as shown in the following example.

***,title
memory,16,m            !allocate 16 MW of memory
geometry={...}         !define the nuclear coordinates
basis=vdz              !Select basis set
hf                     !Perform HF calculation
ccsd(t)                !Perform ccsd(t) calculation

The amount of memory needed depends on the basis set, the symmetry of the molecule, and the methods used, and therefore it is difficult to predict it in advance. Most calculation run with 16 MW or less, but in big cases with low symmetry more may be required. A rather safe choice is to specify 64 MW, but of course this requires that your machine has sufficient memory (in this case more than 512 MB). The memory can also be given using the -m option on the molpro command line, see section 3. It a memory card is given, it has preference over the command line option.