quaternions

 hello all
 i am using the leapfrog\quaternion algorithm from Allen&Tildesley to
 simulate the dynamics of cations in water. with the timestep of 0.3 fs
 i observe a strong increase in energy after about 300 timesteps and
 the waters fly away from the ion.
 doing the same simulation without keeping the waters rigid works
 well.
 has anybody else had a similar experience ?
 thanks for any help,
 gerhard
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 Gerhard Bischof            E-mail:Gerhard.Bischof : at : uibk.ac.at
                    Tel:<0043>512-507-5154
                    Fax:<0043>512-507-2934
 Universitaet Innsbruck
 Inst. f. Allg., Anorg. und Theor. Chemie
 Innrain 52
 A-6020 Innsbruck Austria
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