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Message-ID: <4669A73A.9040708@gmail.com>
Date: Fri, 08 Jun 2007 14:00:10 -0500
From: Jeff Hammond <jeff.science@gmail.com>
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To: Txema Mercero <jm.mercero@ehu.es>
CC: nwchem-users@emsl.pnl.gov
Subject: Re: [NWCHEM] CCSD(T) Error
References: <200706011413.09792.pobmelat@sq.ehu.es> <200706082025.05109.jm.mercero@ehu.es>
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Txema,

The old CCSD(T) code uses the orbital basis, whereas the new CCSD(T) 
uses the spinorbital basis, which is twice as large.  The old CCSD code 
uses less memory at the expense of versatility - it cannot do open-shell 
systems like the TCE can.  The '2eorb' option can reduce a good portion 
of the memory usage within the TCE, but not enough in your case, it 
would seem.

NWChem's coupled-cluster codes are wicked fast compared to other codes 
because they run in memory instead of using disk.  You can make NWChem 
slow like the others if you choose an IO option which writes to disk :)

As Dunyou pointed out previously, if you run with 8 cores, each one 
expected to have ~16 GB of memory.  Your job succeeded likely only 
because the actual memory usage did not exceed the physical memory.

Jeff

Txema Mercero wrote:
> Hello again,
> 
> I finally was able to run the CCSD(T) calculation, 
> but using the old ccdst code:
> 
> ccsd
> freeze core atomic
> end
> task ccsd(t)
> 
> using the the following memory allocation, on a 16GB of RAM,
> 8 opteron cores node:
> 
> memory stack 7500 mb heap 500 mb global 7500 mb
> 
> I was happily surprised, because it was expectacularlly faster than 
> other QM codes I tested.
> 
> But still I am wondering if I was able to run the calculation using
> the old ccsd code, shouldn't I be able to reproduce it on trhe same machine
> with the new TCE code?
> 
> Thanks all of you for your help!
> 
> Txema.