

With regards to your recent posting to the CCL:

I think that the predictor-corrector/quaternion subroutines you are
using are guaranteed to exhibit the kind of numerical instability you
have observed when the timestep is "too large." How large "too large" is
will depend entirely on the system you are modeling (a timestep for water
might be overkill for handling, say, liquid argon). 

This is based on limited experience (i.e., I haven't implemented the
subroutines in Allen/Tildesley you are using). I will be interested to
hear if someone tells you differently.

Best wishes!

robert topper

 Prof. Robert Q. Topper               internet:   [email-masked]
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