Memory Issues

Introduction

When running large calculations (or when running on a machine with a small amount of memory available) You may get memory allocation errors. Depending on the point in the code where the failure occurs, the message may be rather different, and the best course of action could be different. Something like this:
**** error code -1 from mndo97 ******
...hybrid.calc/mndo/hybrid.calc/================= Tstep:    0.0 Ttot:  487.4 ==
...mndo/hybrid.calc/mndo/======================== Tstep:    0.2 Ttot:  487.6 ==
...mndo/hybrid.calc/mndo/[mndo97]================ Tstep:    0.0 Ttot:  487.6 ==
...mndo/hybrid.calc/mndo/[mndo97 exit -1]======== Tstep:    0.0 Ttot:  487.6 ==
May happen if the operating system cannot start a program, in this case MNDO.

DL_POLY

Memory is dynamically allocated. Most of the settings must be left unchanged, but you can vary The mxlist setting if you are using a non-periodic system using the mxlist= parameter. This controls the neighbour list length (maximum number of entries per atom). If you use a small cutoff you can therefore get away with a a smaller value here. If the neighbour list space is too small you will see something like the following:
  mxlist must be >=         1381


 DL_POLY terminated due to error   110


 error - neighbour list array too small
 ** EXITCOMMS **

Remember that the mxlist requirement will change during a run, so to be safe some extra memory should be allocated.

GAMESS-UK

Dynamically allocated, using memory= argument to GAMESS-UK interface.

HDLCOpt and newscf

The memory error messages from HDLCOpt look like this:
'Insufficiant room on stack'
and
'Insufficiant space on heap'
The memory is statically allocated, Controlled by matrix.fh in chemsh/src/quasi/matrix.fh.

Note that when the parallel code is compiled with the GAMESS-UK code linked in, and the GAMESS-UK option newscf is used, the file chemsh/GAMESS-UK/newscf/matrix.fh must have a consistent value, since the same stack/heap is used by the newscf module on gamess.

The memory requirements of hdlcopt can be reduced by specifying the memory parameter.





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