CCL:Problem with SCF convergence in AMPAC

From: Mr Andrew D Allen <chp1aa -8 at 8- surrey.ac.uk>
Subject: CCL:Problem with SCF convergence in AMPAC
Date: Mon, 11 Apr 94 14:10:23 BST

 I am running AMPAC v2.1 and have run into problems with SCF convergence. I have
 a large, ~60 atoms, molecule which converges OK if carry out a geometry
 optimisation on all coordinates. The problem arises when I try to constrain the
 optimisation by flaging some of the bonds, angle and torsions to not be
 optimised.
         Has anyone experienced this problem with Semi-emp, or QM methods in
 general, and has anyone any possible ways to overcome the problem. I would like
 to avoid doing a full geometry optimisation for the molecule due to its size.
 Andy.
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