Subject: Re: CCL:RO jobs on unsaturated organometallics

From: George Vacek <[email-masked]>
Date: Mon, 6 Dec 1999 20:29:40 -0800 (PST)

%% "Eric S. Ball" wrote:
%% > I'm having great difficulty getting convergence for my
%% > restricted open-shell DFT jobs on coordinatively unsaturated
%% > iron compounds.  I'm using Jaguar for these (rob3lyp/lacvp**),
%% > and I've used G94/98 in the past, so suggestions pertaining to
%% > either package would help.  In Jaguar I've used vshifts of 0.2 -
%% > 1.0; accuracy settings (iacc) of quick, medium, and ultrafine;
%% > As per hints in the manual I tried iacc=1 (ultrafine grids) with
%% > the lac3vp** basis (largest available) and etot simply oscillated.

%% Richard P. Muller wrote:
%% I can't speak for Gaussian, but this is a well-known problem in Jaguar
%% for DFT with transition metals. Schrodinger is working on a solution,
%% and I sent them some of our group's most catastrophic convergence cases
%% to test it on.

Convergence difficulty for transition metal containing systems is a
well know issue which affects all QM packages.  As Rick says, here at
Schrodinger we've been working to fix that problem.  For metal
clusters, we're getting close to a great solution, thanks in part to
Rick's catastrophes.  And for organometallics, we've already pretty
much nailed the solution, which you have access to if you are using
Jaguar 3.5.  I'll give more on it below.

As Dale Braden pointed out the best thing to do is email your Jaguar
input files to [email-masked].  Then we'll be able to give you
more specific advice for your exact system.  Short of that, here is 
some general advice, much of which is applicable to any QM package.

Even without the complications of transition-metals in the system,
both the numerical accuracy of DFT and additional basis functions can
make SCF convergence more difficult.  Dale touched on the basis set
issue and Rick on the DFT one, so I won't go into the nitty gritty,
but you should try to first converge the SCF wavefunction with HF
LACVP.  When that wavefunction converges, you can use the wavefunction
in the restart file as a starting guess for a HF LACVP** calculation.
When that converges, restart for DFT LACVP**.  This step-by-step
process is much more likely to succeed.  It also makes it easier to
see which aspect of the calculation (orbital occupations vs. DFT grids
vs. basis set) is causing the convergence difficulties, which in turn
makes it easier to decide which added flags are expected to help the
most: choosing a different convergence scheme, virtual orbital level
shifting, or finer DFT grids.

For Jaguar, the use of and flags for choosing convergence schemes,
virtual shifting, and DFT grids are described in the manual,
especially on pp. 124-6.  I think you are already familiar with some
of the flags, and Dale and Rick have mentioned some others.

Finally, as I mentioned above, Jaguar also provides another unique
feature to improve SCF convergence (both HF and DFT) for some TM
systems.  We realized that most poor convergence of these systems was
due to a really poor initial guess wavefunction (both orbital shapes
and occupations).  So we developed an algorithm based upon
ligand-field theory that creates a high-quality initial guess
specifically designed for organometallic systems.  The success rate of
this initial guess is phenomenal compared with the Huckel guess, that
is used in Gaussian, for instance.  Use of this feature in Jaguar 3.5
is also described on pp.124-6 of the User's Manual.  The method and
some results are published in: G. Vacek, J.K. Perry and J.-M. Lanlois,
Chem. Phys. Lett., 310 (1999) pp. 189-94.

Regards,
George

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George Vacek                    + Schrodinger, Inc. 
(503) 299-1150                  + 1500 SW First, Suite 1180
[email-masked]           + Portland, OR 97201
http://www.schrodinger.com/~vacek/ 

As the critic gained ascendancy in theatre and concert, the 
journalist in the schoolroom, and the newspaper in society, 
art degenerated into the lowest kind of amusement and esthetic 
criticism into the cement of a social group that was vain, 
distracted, egotistic, and totally unoriginal 
-- Friedrich Nietzsche "The Birth of Tragedy" 1872
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