Subject: Summary of GAMESS gradient problem!

From: Ralf Oestereich <[email-masked]>
Date: Sat, 4 Jun 94 16:31:27 MESZ

Dear netters,

This is a summary of the responses to my question concerning
GAMESS. To remind you, my question was why GAMESS terminates 
the calculation with an error like: Gradient vector to big.

Thanks to everyone who helped us and spend time with our
problem. You really help us!

>From [email-masked] Tue May 31 14:04 MES 1994

Ralf,
  One large improvement would be to add d-functions on Si
and Cl (3-21G*).  Such a small and inflexible basis set
needs the polarization functions.  GAMESS may do this for
you, but I can't tell from your message.
Good Luck,
J. D. Evanseck

>From [email-masked] Tue May 31 14:59 MES 1994

Sehr geehrter Herr Oestereich,
>...my problem 

... bedeutet, dass der Gradient der Totalenergie bezueglich der 
Kernkoordnaten waehrend der Optimierung zu gross geworden ist (FMAXT-Parameter).

> 
> As input with use coordinates which are optimzed with ALCHEMEY
> (PC-Windows Version), and then simply translate them, so that
> the first Silicon lies at 0/0/1.52.  At least out input-file:
> 

... das scheint mit sehr problematisch zu sein: Kommen den vernueftige
Strukturen fuer Si-Verbindungen mit ALCHEMY heraus? Mit welchen Kraftfeld
rechnet ALCHEMY? Vielleicht ist es besser, mit einem semi-empirischen
Hamilton-Operator (AM1, PM3) vorzuoptimieren (?!).

Haben Sie es auch schon 'mal mit einer Dichtfunktionalrechnung (Programme
wie DGauss oder DMol, haben wir auf unserer Cray)  versucht?
Falls es Sie interessiert, kann ich Ihnen Kontaktaddressen von Kollegen
nennen, die auf diesem Gebiet auch Rechnungen durchfuehren.

> 
> What must we change, to calculate the molecule?
> Is our basis-set okay?
> Why does GAMESS terminate, what does it mean, if the
> gradient vector is to big?

... - neue und/oder "bessere" (im Sinne der qm-Niveaus) Startgeometrie 
    - Basissatz fuer das erste Scannen der Potentialhyperflaeche OK

>From [email-masked] Tue May 31 15:01 MES 1994

	Maybe your input is in bohr and the program expect them
as angstrom? Otherwise, to force the calculation to proceed,
change the FMAX in routine statpt.src and recompile this
link.
	Frank

>From [email-masked] Tue May 31 15:20 MES 1994

Lieber Herr Oesterreicher,

max. Gradient out of range bedeutet ganz einfach, dass die
Geometrie so schlecht ist, dass man mit den so berechneten
Gradienten keine Geometrieoptimierung machen kann.
Was Sie einmal anschauen sollten im Output, welche Koordinaten
da so schlecht sind. Vor der Linie die Sie uns geschickt haben
ist der Output mit 3 Gradienten per Atom. Vielleicht schaffen sie
es damit, die Geometrieoptimierung zu starten in dem
Sie schon einmal das oder diese Atome in die angezeigte Richtung
schieben. Versuchen Sie das vielleicht zuerst semiemprisch,
PM3 sollte mit den Si-Dingern noch einigermassen zurechtkommen.

                                      mit freundlichen Gruessen
                                        Hans Ulrich  Suter

>From [email-masked] Tue May 31 15:25 MES 1994

First, I would suggest defining a z-matrix for your system.  I think
that GAMESS will guess a reasonable hessian, based on some empirical
rules, if internal coordinates are available.  When only using
cartesians GAMESS may be forced to start with a strictly diagonal
hessian, so that the first optimization steps are merely steepest
descent.

If that fails, you might try an STO-3G calculation with an analytical
hessian, and use the resulting geometry and hessian as input to the
3-21G run.

It might also help to pick a few symmetric geometries and optimize
them, then distort them just slightly and re-run without symmetry
constraints.

>From [email-masked] Tue May 31 15:32 MES 1994

Hallo Ralf,

nach meiner Erfahrung mit GAMESS bei der Optimierung von Strukturen sollte
man die mit einem Molekuel-Editor (wir benutzen HyperChem) erzeugten
Strukturen zuerst mit einer kleinen Basis, oder besser mit einer
semiempirischen Methode vorminimieren.

Ich minimiere zuerst mit dem standard MM2+-Kraftfeld (HyperChem), danach mit
der PM3-Methode (MOPAC, oder auch GAMESS). Erst danach benutze ich die
abinitio Basissaetze (3-21G, dann 6-31G) zur Minimierung.

Dieses Vorgehen ermoeglicht nicht nur eine fehlerfreie Minimierung (keine 
Aussetzer mit "Gradient to large"), sondern spart auch Rechenzeit.
Man rechnet erst dann mit einer aufwendigere Methode weiter, wenn schon eine
gut minimierte Struktur vorliegt.

Ich hoffe ein wenig geholfen zu habe.

        -------------------------------------------------------------

>From [email-masked] Tue May 31 15:45 MES 1994

> MethylChlor2-Sil-Sil-MethylChlor2  RHF/3-21G, Symmetrie C1
> C1
> SILICON  14.0      0.0000   0.0000   0.8094
> SILICON  14.0      2.2068   0.2512  -0.7219 
> CHLOR    17.0     -0.4898  -0.7698  -0.6029 
> CARBON    6.0     -0.0041  -0.4822   1.8261 
> CARBON    6.0      2.2029   0.9573  -2.4745
> CHLOR    17.0      2.7256   0.9298   0.0391
> HYDROGEN  1.0      1.6782   1.9252  -2.4824
> HYDROGEN  1.0      1.6753   0.2673  -3.1496
> HYDROGEN  1.0      3.2307   1.105   -2.843 
> HYDROGEN  1.0     -1.0186  -0.6726   2.1871
> HYDROGEN  1.0      0.4482   0.3304   2.421 
> HYDROGEN  1.0      0.6092  -1.3903   1.9685 
> CHLOR    17.0     -0.5346   0.9436  -0.1505 
> CHLOR    17.0      2.7156  -0.7913  -0.6104

Hallo Ralf!

Ich habe grosze Zweifel an diesen Koordinaten.
Schau sie Dir einmal mit dem MOLPLT an!

Abgesehen vom Si-Si-Abstand, sind fast alle Bindungen viel zu kurz:
Die kurzeste Si-Cl Bindung ist gar nur 1.14 A (2-6) lang! Auch die 
Si-C Bindung mit 1.13 A (1-4) ist rekordverdaechtig. Letztlich ist auch
der Cl-Cl-Abstand von 1.77 A (3-13) bemerkenswert (im Cl2 ist es, glaub'
ich, knapp unter 2 A).
Auszerdem stimmen die Winkel am Si nicht so recht.

Ich wuerde mal die Herkunft dieser Koordinaten genau ueberpruefen!

Viel Erfolg,

Gernot

>From [email-masked] Tue May 31 18:40 MES 1994

Dear Ralf,
  I am responding to your question on CCL about GAMESS.  Since the
gradient is that large (>3!), it means that the starting geometry is
VERY bad (at least for the level of theory tried).  I ran an
EXETYP=CHECK run and looked at the internuclear distances.  The Si-Si
distance is almost 3 Angstroms (a "normal" Si-Si single bond is about
2.4).  The Cl's seem to be very close together.  I used MOLPLT
(the graphics package that comes with GAMESS) and found that the
molecule is very "strange".  The geometries around the Si's are
rather flat and one of the methyl groups looks like it is
trying to leave the molecule.
  I would suggest bringing the Si's closer together, pyramidalizing
the other substituents around the Si's and giving "reasonable" distances
for the substituents to Si.  In other words, I think the program you
used must have given you a bad geometry.  It might be easier to just
put in a guess by hand.
  Hope this helps.

>From [email-masked] Tue May 31 18:51 MES 1994

> 
> Dear netters,
> 
> we have the following problem with GAMESS (US):
> 
> While calculating the molecule:
> 
> 
    It means the initial geometry is too bad to optimize. Particulary
you should be careful about bond length. In this case, I found the Si-Cl
bond lengths are too short. It's standard length is somewhere around
2.1 angstrom. So, the following input will work.

$data
1,1-dimethyltetrachlorodisilane
c1
Si
Si 1  2.4
C  1  1.88  2 110.0
C  2  1.88  1 110.0  3  180.0
Cl 1  2.1   2 110.0  3  120.0
Cl 1  2.1   2 110.0  3 -120.0
Cl 2  2.1   1 110.0  4  120.0
Cl 2  2.1   1 110.0  4 -120.0
H  3  1.1   1 110.0  2  180.0
H  3  1.1   1 110.0  9  120.0
H  3  1.1   1 110.0  9 -120.0
H  4  1.1   2 110.0  1  180.0
H  4  1.1   2 110.0 12  120.0
H  4  1.1   2 110.0 12 -120.0
 $end

Of course you need to put COORD=ZMT in $contrl group and I think use
NZVAR=36 is a good idea. Also if you are seeking global minimum,
starting another optimization with torsion of C-Si-Si-C set 60 is
necessary.

Hideaki Shimizu

>From [email-masked] Tue May 31 21:06 MES 1994

Dear Ralf:

	A very large gradient is usually indicative of a bad starting 
geometry.  I recommend that you re-check your input structure -- either
graphically or by looking at the distance matrix in the GAMESS output.

			Best regards,
					Jan Jensen
>From [email-masked] Wed Jun  1 10:46 MES 1994

Why don't you use a good Z-matrix? Then you can see which bonds/angles/torsions

run away from the optimum. The molecule doesn't seem too complicated.
It means, that your optimization diverges; because the target of a gradient
optimization is to find the stable point (or one of the stable extrema)
where the gradient vector is zero. So the program notices that something
is very wrong and terminates, when it sees the gradient increases abnormally.

BTW what version of GAMESS do you use??? I've never seen such a weird input
file :-) Is it the GAMESS-US version?
I haven't looked at your problem more closely because I don't have the time
but I wish you good luck with it.
Greetings,
Frits

>From [email-masked] Thu Jun  2 19:37 MES 1994

I read your message on the computaional network.  I seem to encounter similar 
problems with gamess when I try to optimize geometries of some clusters.
I was wondering if you received any useful responses.  Please reply to 
[email-masked].

Thank you for your help.

Raji