Insuffcient virtual memory

What to do about insufficient virtual memory errors? I seem to be getting them in the geometry optimization part of large simulations of 500+ atoms or simulations where a molecule and a cluster model of graphene are separated by a large distance of 10A. I am using 6-31G* or less with PBE + D2 level of theory. I tried increasing MEM_TOTAL and MEM_STATIC.

I believe that what you are experiencing is a known problem with generation of delocalized internal coordinates for large systems with lots of nonbonded interactions. (It is specfically for nonbonded cases, e.g., I have seen with pi-stacked arenes but not on proteins fragments of comparable size.) The code generates a relatively large number of primitive internals in the nonbonded cases and runs out of memory in the cartesian --> internal transformation. If you cannot increase memory to make it go away, then the only workaround at this time is to use Cartesian coordinates for the optimization (GEOM_OPT_COORDS = 0). That avoids the memory bottleneck at the cost of taking a much larger number of optimization steps.

For developers, this is Trac ticket #2318.

Hi jherbert. The GEOM_OPT_COORDS = 0 fix worked great! Thanks for the reply.