Extended System Dynamics Methods


Grand Canonical Ensemble Molecular Dynamics

Extended system dynamics method for closed systems (with fixed number of molecules) has been developed and widely used during 80's. A similar approach is taken to extend a system with a variable number of molecules. In this simulation method, the number of molecules become a variable (instead of an integer, a real variable is used to represent the number of molecules at any instant). Integer portion represents full atoms/molecules, whereas the remainder represents the strength of coupling of a fractional atom/molecule to the rest of the system. The chemical potential drives the number variable through a dynamical equation of motion. At integer values of number variable a new fractional atom/molecule is initiated while the old one either becomes a full atom/molecule or decouples from the system.

Equations of motion for "coordinates" and "momenta" of atoms and the additional extended system variables are obtained from the extended hamiltonian.

Recent modifications to the hamiltonian approaches for GCMD simulations involved addressing the ideal gas contribution [4,5].


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  2. T. Cagin and B. M. Pettitt, Mol. Phys. 72, 169 (1991).
  3. J. Ji, T. Cagin and B. M. Pettitt, J. Chem. Phys. 96, 1333 (1992).
  4. S. Wearingshe and B. M. Pettitt, Mol. Phys. (1994)
  5. C. Lo and Palmer, J. Chem. Phys. (1995).