On Thu, 22 May 2003, Alex Angerhofer wrote:
> I've tried to calculate the g-tensor of an anion of a chlorophyll
> derivative (74 atoms, containing Mg, O, N, C, and H). The SCF part runs
> fine, but EPR aborts with an iraloc error:
>
> <May21-2003> <00:06:02> EPR 2002.03 RunTime: May21-2003 00:06:02
> <May21-2003> <00:06:04> >>>> GENPT
> <May21-2003> <00:06:04> Acc.Num.Int.= 6.000
> <May21-2003> <00:06:16> Block Length= 128
> <May21-2003> <00:06:17> >>>> PTCOR
> <May21-2003> <00:06:30> >>>> POT
> <May21-2003> <00:12:21> >>>> SHIFTS
> <May21-2003> <00:12:21> >>>> SIPREP
> <May21-2003> <00:12:21> >>>> EPRPOT
> <May21-2003> <00:19:18> >>>> SISUB1
> <May21-2003> <00:19:18> >>>> SISF1
> <May21-2003> <00:19:18> iraloc: exceeded maximum memory
> <May21-2003> <00:19:18> END

Alex,

Try adding:

   VECTORLENGTH 15

to the SCF (not the EPR!) input, and/or:

   MAXMEMORYUSAGE 512

to the EPR (not the SCF!) input.

Explanation:

For various reasons, EPR uses the same block length for numerical
integration,
as the SCF part. Normally, the SCF part tries to maximize memory
utilization,
by choosing the largest vector length possible. Because EPR tends to
keep somewhat
more data in memory per numerical integration point, it may run out of
memory for
larger systems.

> From the performance point of view, on non-vector platforms there is
> very little
benefit in increasing vector length beyond 20-30 (in fact, this may
even slow the
things down, by making cache less effective).

Serguei

---
Dr. Serguei Patchkovskii
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Fax: +1-(613)-947-2838
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Coordinator of Modelling Software
Theory and Computation Group
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National Research Council Canada
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