Subject: MOPAC-93 memory requirements

From: Victor Anisimov <[email-masked]>
Date: Sun, 19 May 1996 20:15:18 +0400

Dear netters,

Does someone have experience compiling MOPAC-93 for big
dimensions, 100x100, 200x200 heavy and light atoms, for
example. How much virtual space they will reqire?

I'm getting "can't allocate memory" message on FreeBSD
with 400Mbyte of virtual space on hard disk for 100x100 
one.

What is this, low virtual space or Fortran compiler error,
does someone know?

Thanks for any idea.
Victor.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   ***     Institute of Chemical Physics in Chernogolovka     ***
   *                Russian Academy of Sciences                 *
   *                                                            *
   *                   Dr. Victor M. Anisimov                   *
   ***                   [email-masked]                    ***
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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From: "David E. Bernholdt" <[email-masked]>
Date: Mon, 20 May 1996 13:57:22 -0400

I seem to recall that MOPAC 7 compiled for 100 heavy + 100 light atoms
took up about 130 MB on an IBM RS/6000.  Should be able the same on most
other platforms, since most of the space is common blocks, not code.

Is it 400 MB _free_ virtual memory, or 400 MB _total_ VM?  Depending on
what else you're doing on the machine you could have a lot less than 400
free.  Also, trying to run very large memory jobs on my RS/6000, I've had
problems with jobs that apparently should fit comfortably within the free
VM, but not in physical memory.  When I get _closer_ to the neighborhood 
of free physical memory, it works.  I haven't had time to sort this out 
yet, but you could be experiencing something similar.

Hope this helps.
--
David E. Bernholdt                      | Email:  [email-masked]
Northeast Parallel Architectures Center | Phone:  +1 315 443 3857
111 College Place, Syracuse University  | Fax:    +1 315 443 1973
Syracuse, NY 13244-4100                 | URL:    http://www.npac.syr.edu

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From: A J Turner <[email-masked]>
Date: Mon, 20 May 1996 23:32:15 +0100 (BST)

Hi!

I don't know about mopac, but Charmm can do a similar thing.  I think the 
problem is that if the largest single array gets bigger than your 
physical memory, the oppperating system cannot 'break it up'.  This is 
probably a FORTRAN thing, as the arrays are contiguously assigned, rather 
than using pointers to point into blocks a dynamically allocated memory, 
as a C program _probably_ would do (well that's how I'd do it!).

Cheers

Alex

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