Hello,

I have a question concerning generating redundent internal coordinates,

needed for geometry optimization. In my case, I want to calculate

a minimum energy path along an internal coordinate. For this I need to do

several geometry optimization calculations, in which the value of the internal

coordinate will be varied, with each value being kept frozen during the optimization.

At the same time, I have two atoms that I want to freeze completely. I do

this by freezing their Cartesians. Now comes the question: **I would like to**

keep the values of these 6 frozen Cartesians the same at all points along the

minimum energy path. This seems to be not so trivial because, when

I change the value of the frozen internal coordiante (using define), define

also changes the vaules of the frozen Cartesians. I tried to replace the

new values of Cartesians by the old ones (i.e. those I want) and then run

the geometry optimization without repeating define. However, this doesn't work

in all cases. Sometimes when the initial geometry is to bizarre, due to the replacement,

the procedure which does convertion from internal to Cartesians does not converge.

Therefore I wonder if there is another, more appropriate way to keep the same

Cartesians while changing the value of an internal coordiante.

I would appreciate very much any idea/point to solve this difficulty.

Best wishes,

Evgeniy