| 10:32:41 AM PDT - Wed, Apr 18th 2012 |
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Some progress
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Hi Rick,
Initially I thought that perhaps various accuracy aspects of the energy expressions and numerical differentiation play into this problem. So I tried somethings the crank up the accuracy of the energy (finer DFT grids) as well as the gradient evaluation (using a 5 point expression for the numerical gradients) but all to no effect. In particular I noticed that the geometry kept changing rather a lot from point to point.
It seems that this problem is caused by the fact that the system you are studying essentially consists of 2 non-bonded fragments. The Hessian along the coordinates connecting the 2 fragments is virtually 0 causing the optimizer to take rather large steps. So I am currently looking at ways to reduce the coordinate updates in the hope that that will allow the calculation to converge.
Best wishes,
Huub
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