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Date: Tue, 06 Dec 2005 08:26:52 -0500
From: Geoffrey Bowers <gmb189@psu.edu>
Subject: [NWCHEM] Slow Shielding Calculations
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Greetings!  My name is Geoffrey Bowers and I am a student in a solid-state
NMR group that has recently begun using NWChem to calculate electric field
gradient tensors and chemical shielding tensors.  We have version 4.7
running under ECCE on a home-built dual 3.0 GHz Xeon with 3 GB of RAM
running Red Hat Linux WS 3.0.  Thus far, our EFG calculations have been
going very well and running at reasonable lengths of compute
time.  However, we are having trouble with DFT calculations where chemical
shielding is computed as well.  For example, on a cluster of crystalline
celestine (Sr11O40S10), calculating the EFG with RDFT takes on the order of
24 hours on our machine.  Adding the shielding calculations increases the
length of compute time by greater than a factor of four.  We have not even
been able to get any shielding calculations to run to completion with a
simple tri fluoro silane molecule, C5H11F3OSi.  It seems to fail after two
days of compute time with any set of starting conditions.  We seem to get
these delays independent of basis set complexity and whether the SCF is
computed in-core or directly.  It also does not look like the calculation
is using up the available scratch space, so that isn't our bottleneck.

Does it normally take NWChem so long to calculate shielding
parameters?  Has anyone else reported long shielding calculations with a
similar computer setup?  Do you have any suggestions for improving the
speed of our computations on our in-house system?  At this point, we are
just trying to sort out whether it is a computer hardware problem or a
software issue and whether this is the best route to go for our shielding
calculations.  Any advice/insight would be helpful.  Thanks!

Geoff


Geoffrey Bowers
Mueller Group - Solid State NMR
Penn State University
Department of Chemistry
104 Chemistry Research Building, Box 66
University Park, PA  16802
814-863-3577
gmb189@psu.edu
http://research.chem.psu.edu/ktmgroup/

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