Subject: Re: RO jobs on unsaturated organometallics

From: "Jason K. Perry" <[email-masked]>
Date: Mon, 6 Dec 1999 14:35:48 -0800

Dear Eric,

        I just wanted to follow-up on the useful suggestions of Dale
Braden and Rick Muller on how to deal with converging your DFT with
Jaguar.  Dale's suggestion to send the case to [email-masked]
is best.  We're very interested in looking at all cases that appear
problematic - it is a top priority at Schrodinger to ensure our software
products are performing properly for our users.  

In most instances, a simple solution can be found (as I'll detail below).  As
for cases that may be more difficult, we use those as a guide for improving
robustness of the code.  It might be the case that your calculation converges
smoothly in Jaguar v4.0 (now in beta release).

        The manual offers some suggestions on improving convergence of
difficult cases (section 6.3).  Generally we suggest:

        1)  Try setting vshift.  This increases the energy of the virtual
        orbitals such that they mix with the occupied orbitals more
        slowly.  This stabilizes oscillatory convergence.  Usually it's
        sufficient to set vshift to 0.5-1.0 (hartree), but there have
        been a couple rare cases where vshift=2.0 appeared necessary.
        We offer a variable vshift in Jaguar v4.0.  It's more conservative
        in the early iterations, reducing the size of vshift as
        convergence is approached.

        2)  Try changing the accuracy settings.  The default accuracy
        in Jaguar is quick.  Setting the accuracy to ultrafine (iacc=1)
        improves convergence in some cases.  That doesn't appear to be
        the problem here, though.

        3)  Try changing the convergence scheme.  The default is DIIS
        (iconv=1).  A more conservative scheme is GVB-DIIS (iconv=4).

        4)  Try changing the initial guess.  If you can converge the
        HF/LACVP wavefunction, that would probably be your best initial
        guess for the B3LYP/LACVP** calculation.  We've modified the
        default initial guess for organometallics in Jaguar v4.0.  You
        can get this functionality in v3.5 using iguess=25 and an &atomic
        section, as explained in the manual.

I encourage you to try the above options, but please don't hesitate to send 
your input files to [email-masked], so that we could examine them 
ourselves and provide more specific suggestions.

        Hope this helps,

        Jason Perry
        Schrodinger, Inc.
        http://www.schrodinger.com

> Greetings,
> 
> 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.
> 
> If anyone has successfully dealt with a similar situation with
> either Jaguar or G98, I'd love to start a little dialog. 
> If/when I meet with success I'll edit down any conversations to
> the pertinent points and repost them.
> 
> Thanks in advance,
> Eric Ball
> 
> 
> 
> 
> 
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