Re[4]: CCL:GDIIS and Z-MATRIX

[John Lee <g03.-at-.joyie.com>]

Hi Cust.,
 It does help me a lot. I used Int=ultrafine and opt=calcall, with
 tight option. although the RMS Displacement still didn't reach the
 threshold, the RMS force reached. I need to perform a freq calculation
 to make sure it is a minimum. Now all the distances between neighbor
 oxygens are the same (4 water cluster). The distances beteen O-H and
 O...H are also the same.
 Thank you very much.
 Best regards
 John Lee
 Wednesday, October 15, 2003, 9:13:24 AM, you wrote:
 CSD>     My guess is that it was hard because the Berny algorithm needed
 CSD> to have the integration quality improved to go along with the tighter
 CSD> integration criteria and the small forces involved in these clusters.
 CSD>     In such a case I am dubious that GDIIS is really giving you a
 "better"
 CSD> structure, but I can believe it is willing to claim the criteria
 CSD> are met.  It deals better with inaccuracies in the gradient and so
 CSD> I have suggested its use with solvation models and as you can see from
 CSD> the manual with semi-empirical models.
 CSD>     To use the Z-matrix I would recommend you try a couple of
 CSD> approaches.  First use Int=Ultrafine and see if OPT=Tight does not
 CSD> behave better.  Second, I would suggest doing this as OPT=(CalcFC,Tight)
 CSD> if you are starting close to an optimized structure.   Or possibly
 CSD> OPT=(CalcAll,Tight) because the force constants here are small and
 CSD> it is vital to have them correct for the optimization to work.
 >>
 >> Hi Cust.,
 >>
 >> I the simulation of 4-8 water cluster, I want to keep all the
 >> distances between neighbor oxygen the same. However it was hard to
 >> converge with B3LYP 6-311++G** and tight if I didn't use GDIIS. If I
 use GDIIS
 >> the distances will not be the same.
 >>
 >> Thanks for your reply.
 >>
 >> John
 >>
 >> Tuesday, October 14, 2003, 5:27:52 PM, you wrote:
 >>
 >>
 >> CSD>   John,
 >>
 >> CSD>    Why do you need to use GDIIS?
 >>
 >> CSD>    Note that this would break symmetry only if you are using
 the Z-matrix
 >> CSD> to define symmetry which is not really in the molecule?
 >>
 >>
 >> >>
 >> >> Hi CCLers,
 >> >>
 >> >> Z-matrix optimization only work with Berny algorithm.
 >> >> What if I have to use GDIIS and still want to control the
 zmatrix
 >> >> symmetry. Is there a way to do it?
 >> >>
 >> >>
 >> >>
 >> >> --
 >> >> Best regards,
 >> >>  John
 >> >>
 >> >>
 >> >>
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 >>
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 >>
 >>
 >> --
 >> Best regards,
 >> John Lee
 >>