\a/Victor Rosas.
Thank you for your help. Do you mean if I us= e a well suitable optimizer the Gradient Norm will not be as high as I have= gotten using EF? Anyway I will try that and let you know what happen. I wo= uldn't like to use "TS" because I intend to compute for the ground states. = Or do you think using "TS" would not have effect on Ground State calculatio= ns?
Thanks.

Olasunkanmi Lukman Olawale

Current Address:
Department= of Chemistry,
Obafemi Awolowo University,
= Ile-Ife, Osun Sta= te.
Nigeria.

+234-0-80-52401564 Or +234-0-80-67161091
=

<= div style=3D"font-family: times new roman,new york,times,serif; font-size: = 12pt;">

From: Victor Rosas Garcia rosas.victor _ gmail= .com <owner-chemistry\a/ccl.net>
T= o: "Olasunkanmi, Olawale Lukman " <walecomuk\a/yahoo.co= .uk>
Sent: Tue, 8 Fe= bruary, 2011 16:53:53
Subject: CCL: dissenting results

Just do what the error message says "REDUCE = GRADIENT USING 'TS' OR OTHER GEOMETRY OPTIMIZER". You should make sur= e you are using PRECISE and maybe try the different optimizers. The default= is "EF", but you can try BFGS or DFP. See which one works best.
=0A
= I wouldn't worry too much about the different heats of formation because th= e geometry is essentially unconverged, so none of those numbers means much = anyway.

Hope this helps.

Have a nice day!

=0AVictor

2011/2/7 Olasunkanmi Lukman Olawale walecom= uk(a)yaho= o.co.uk <owner-chemistry,+,ccl.net>
=0A

Thank you Victor. I g= ot your explanation but something still baffles me.
=0AIf I run the MOPA= C job without the THERMO key word I will get some parameters: e.g. final he= at of formation, total energy, electronic energy etc.
But, with THERMO = key word, most often I experience this kind of warning/error:
=0A** GRAD= IENT IS TOO LARGE TO ALLOW FORCE MATRIX TO BE CALCULATED, (LIMIT=3D10) ** EITHER ADD 'LET' OR REDUCE GRADIENT
USING 'TS' OR OTHER GE= OMETRY OPTIMIZER

It will however give a value for the heat of format= ion again, this time around somehow different from the former value. A typi= cal case for 1,10-phenanthroline:
=0A FINAL HEAT OF FORMATION =3D&n= bsp; 81.10951 KCAL/MOL =3D 339.36220 KJ/MOL
without using the THER= MO keyword.

AND

HEAT OF FORMATION=0A =3D   &nb= sp; 89.398345 KCALS/MOLE
when the THERMO keyword was used.
So w= hat do you suggest I do?

Olasunkanmi Lukman Olawale
=0ACurrent Ad= dress:
= Department of Chemistry,
Obafe= mi Awolowo University,
=0AIle-= Ife, Osun State.
Nigeria.
=0A
234-0-80-52401564 Or +234-0-80-67161= 091
=0A

=0A
From: Victor Rosas Gar= cia rosas.victor*gmail.com <owner-chemistry]|[ccl.net>
=0ATo: "Olasunkanmi, Olawale Lukman " <walecomuk]|= [yahoo.co= .uk>
Sent: Fri, = 4 February, 2011 13:53:11
=0ASubje= ct: CCL: dissenting results

GNORM =3D 109.40376?
That is=0A *huge*. How did you get such a specific number= , by the way?

Anyway, you should be careful with the use of LET.&nbs= p; From the manual (http://www.openmopac.net/manual/index.ht= ml):
=0A=0A
    Now LET means essentially = "I know what I'm doing, override safety checks".
=0A
   = ; Currently, LET has the following meanings:
=0A
&= nbsp; 1.In a FORCE calculation, it means = that the supplied geometry is to be used, even if the gradients are large.<= /dt>=0A
So you are giving MOPAC a geometry that is not converged, and t= elling it to do THERMO no matter what. You could try doing the optimi= zation using PRECISE and then do the FORCE calc without LET and GNORM.
= =0A
The manual is your friend!

Hope this helps and have a nice d= ay

Victor

2011/2/3 Lukman Olawale Olasunkanmi waleolasunkanmi= =3D=3D=3Dgm= ail.com <owner-chemistry**ccl.net>
=0A=0A
Thank you= .
Here are typical results:
After geometry optimization without any s= pecial keyword:
=0A=0AFINAL HEAT OF FORMATION =3D 40.08240 KCAL/MO= L

With keyword "thermo", and LET GNORM =3D 109.40376

=0AHEAT= OF FORMATION =3D      43.366029 KCALS/MOLE
Sometimes the difference may be up to 10kcal/mol for some calculations. Kindly give me an advice on it.
thanks.

wrote:
=0A=0A=0A
=0ASent to CCL by: "Close, David M." [CLOSED!A!mail.etsu.edu]=0AThis is very interesting. But you need to tell us how much the nu= mbers differ. I can see how sometimes very small difference could ari= se from coding errors arising from one subroutine using a double precision = variable, and another subroutine using the same variable with a different w= ord-length. But these would be very small differences. Give us = an example of how big the differences are, and what keywords are used to co= ntrol the accuracy of each SCF cycle.
=0A=0A=0A=0A Regards, Dave C= lose.
=0A
=0A-----Original Message-----
=0A> From: owner-chemis= try+closed=3D=3Detsu.edu-$-ccl.net [mailto:owner-chemistry+closed=3D=3Detsu.edu-$-ccl.net] On Behalf Of Lukman Olawa= le Olasunkanm waleolasunkanmi:gmail.com
=0A=0A=0A=0ASent: Tuesday, February 01,= 2011 8:43 AM
=0ATo: Close, David M.
=0ASubject: CCL: dissenting resu= lts
=0A
=0A
=0ASent to CCL by: "Lukman Olawale Olasunkanm" [waleol= asunkanmi#,#gmail.com]
=0AHello everyone,
=0AI usually run my MOPAC job twic= e: first for ordinary optimization from which I normally get the GNORM valu= e ( and H.O.F., dipole moments, HOMO-LUMO, COSMOS Area and volume etc.), an= d second for the thermo values (with the specified value of the GNORM using= the LET keyword). I discovered that the values got for the common paramete= rs like H.O.F, dipole moments etc. in both cases differ.
=0A=0A=0A=0AWha= t can you advise me to do please?
=0AThank youhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_u= nsub.shtmlhttp://www.ccl.net/spammers.txt
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-- =
Olasunkanmi Lukman Olawale

Department of Chemistry,
Obafemi Awolowo Uni= versity,
=0A=0A=0AIle-Ife, Nigeria.
+234-08= 052401564

"Improving our own attitudes and our own state of mind takes time. Haste= and impatience can only defeat our purposes."
=0A=0A=0A
= =0A

=0A
=0A

=0A=0A=0A=0A

=0A