Subject: MOPAC Error Message.

From: [email-masked] (Jason Lye)
Date: Fri, 27 Oct 95 19:00:21 -0400

Dear Net-surfers,

I am attempting to use MOPAC 6.0 to construct Jablonski diagrams for several
dyes, and for now I am interested in the singlet excited state energies.  I am 
using the PM3 optimised structure (gradient approx.=1) as my input for several 
SCF energy calculations, to obtain excited state energies in which I used the 
following keywords (PM3): 

SINGLET C.I.=7 ROOT={n+1}             	Where n=1,2,3,4,5,6
					For S1, S2, S3, respectively.

Unfortunatly, in the case of several structures, MOPAC stopped and returned an 
error message, viz:

`Degenerate energy levels detected in the MECI.  Some of these levels would be 
treated by MECI, while others would not.  This would lead to non-reproducable 
electronic energies.
Job stopped;  to continue specify GEO-OK."

I added the keyword PRECISE to try and tighten the SCF convergence criteria, 
however, this seemed to have no effect.

Reluctantly, I added the keyword GEO-OK and the energy levels were returned as 
expected, but.......

*  Could someone please tell me:

a)	What does the abovementioned error message really mean?  Does it refer 
	to M.O.s or states or something else in the C.I. calculation?
b)	How can I avoid generation of the message?
c)	What are the consequences of specifying GEO-OK?

I have also come across the same scenario when dealing with excited state 
geometry optimizations in the past, and once again, the only way around them 
seemed to be to use GEO-OK.  I am concerned that by using this keyword, I am 
forcing the calculation to continue to completion when something is inherently 
problematic in my structure.

I intend to summarise my responses to this question and post it to the list, as
I did before.

Thank you, 
Jason.

_______________________________________________________________________________

Jason Lye,                       |    
Dye Synthesis Research Group,    |    
College Of Textiles,  Box 8301,  |     "If we did'nt have any bones, 
North Carolina State University, |      we would have to live in a bucket."
Raleigh, N.C. 27695 - 8301       |     
                                 |      
      Ph:   (919) 515-6615       |                     
      [email-masked]           |         
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