Subject: CI Geometry Optimization Error in MOPAC2000

From: Damian Allis <[email-masked]>
Date: Mon, 21 Aug 2000 15:38:29 -0400

Greetings all!

	In trying to optimize the ground state geometry of a charge transfer
species in MOPAC2000 using CI, I get the following error for the C.I.=4 case:

THE BAB MATRIX OF ORDER 11 IS SINGULAR IN DERI2
 THE RELAXATION IS STOPPED AT THIS POINT.
 RELAXATION ENDED IN DERI2 AFTER 10 CYCLES
 REQUIRED CONVERGENCE THRESHOLD ON RESIDUALS = 0.000010000
 HIGHEST RESIDUAL ON  1 GRADIENT COMPONENTS =  0.811538357
 ELAPSED TIME IN RELAXATION      12868.881 SECOND

	The AM1 optimization goes without a problem, and the C.I.=2
optimization, while the heat of formation is 40 kcal/mol higher and the
dipole is 1/10 that of the CI-less AM1 calculation, works fine as well
(all things considered).  It is at the case of C.I.=4 that my problems
start to arise.  I've tried a variety of MECI and converger keyword
options, but have had no success.

	Is there something someone's found to get around this problem?  Or is
this a new one on everyone else, too?
				
									thanks in advance,
                                                Damian

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