A new approach to constrained molecular dynamics

The internal motion of a semirigid molecule is described in terms of variat ions of intramolecular distances, valence angles, out of plane wagging and torsions. Constraints may be imposed to any selected group of these paramet ers and the reduction of the number of degrees of freedom is realized throu gh a suitable basis change, splitting the space of displacements into two o rthogonal subspaces, one of them spanned by the coordinates forced to vanis h. The treatment differs from the previous ones, which all rely on the Lagr angian A method and thus dispense with the definition of unconstrained coor dinates, which do not eventually appear also in the expression of the const rained Cartesian displacements given here. It turns out that the previous S HAKE algorithm of the constrained dynamics include unnecessary calculation at each time step. (C) 2001 Elsevier Science B.V. All rights reserved.