Subject: Mopac Calculations on Benzoyloxy Radical

From: [email-masked]
Date: Wed, 1 Dec 1993 12:43:59 PST

I am completing a table of calculations on a series of radicals
including the benzoyloxy radical C6H5CO2(.) using the default (Dewar`s
half-electron) protocol in Mopac6.  Although these calculations proceed without
incident for most systems, the benzoyloxy system refuses to converge to a
minimum stationary state using keywords:

	AM1 PRECISE EF GNORM=0.01 GRAD (RECALC=1)

	I have tried all manner of options for finding the minimum:
	NLLSQ gives a saddle point as the stationary point
	UHF also does not converge
	BFGS does not lead to convergence

	It seems clear that part of the problem is the SCF procedure since
SHIFT, PULAY and the Camp-King SCF convergers are invoked.  I have extended the
systems to thiobenzoyloxy  C6H5COS(.) and acetyloxy CH3CO2(.) but these also
give me the same problem.
	Particularly curious to me is the observation that if one uses the PM3
Hamiltonian, the benzoyloxy system does converge to a minimum!  However,
starting the AM1 calculation using the PM3 minimized geometry again leads to
convergence failure.
	If anyone has any suggestions on how I might proceed.  I would be
grateful for your input.
		Thank you for your help,
		Peter Kazmaier
		Xerox Research Centre of Canada
		[email-masked]