Parrinello-Rahman

Martondk, R. Laio, A. Parrinello, M., Predicting crystal structures the Parrinello-Rahman method revisited, Phys. Rev Lett. 2003, 90, 075503-01... 

The Lagrangian L for Lees-Edwards boundary conditions combined with Parrinello-Rahman fluctuations for the cell geometry now reads as follows ... 

Sprik et al, 1993 Signorini et al, 1990), a typical example being the orientational disorder associated with NH in NH Br. Detailed simulations have been reported on (NaCN),, t(KCN),t and other mixed alkali halides and alkali cyanides. Other systems studied include potassium and calcium nitrate crystals and their mixtures. The transition from the crystalline to the superionic conductor phase in solid electrolytes has also been successfully investigated. Molecular dynamics studies of Agl were carried out by Parrinello, Rahman Vashishta (1983). LijSO has been investigated by molecular dynamics by Impey et al. (1985). Here, the Li ions become mobile at high temperatures. The ions exhibit orientational disorder and the orientational... 

Parrinello-Rahman method. The constant pressure MD formulation of Andersen (4) provides a method for permitting the variation in the volume of the simulation cell. Parrinello and Rahman (5, 14, 15) generalized Andersen s method to include variations in the volume as well as the shape of the simulation cell. In the Parrinello-Rahman formulation, the simulation cell is represented by three vectors, a, b, and c. The lagrangian is given by... 

Carbon tetrafluoride. Carbon tetra-fluoride, which undergoes a transition to a plastically crystalline (orientationally disordered) phase, has been investigated by the Parrinello-Rahman molecular dynamics method under constant-pressure conditions (6). A simple intermolecular potential model of the Lennard-Jones form was derived by taking into account the experimen-... 

Solid-state phase transitions often involve deformation of the unit cell along with rearrangements of the molecules inside the unit cell. Therefore a simple constant-pressure simulation which allows only isotropic expansion or contraction of the unit cell may not be able to reproduce all of the aspects of a solid-state phase transition. The technique of Parrinello and Rahman [160] introduces a time-dependent metric tensor in the Lagrangian of the system, which allows changes of both volume and shape of the xmit cells. As such, simple solid-state phase transitions can be directly simulated with this technique. However, this method cannot be used for solid phases with very different unit cells.[145] The orientational order-disorder transitions in the solid state in some cases occur with little change in the unit cell parameters or molecular rearrangements. These orientational transitions are suitable for the Parrinello-Rahman technique.[161]... 

Unfortunately, as originally presented, the NEB method cannot be used to study mechanochemistry in the bulk, as there is no way to allow the simulation cell to change in response to shear or compression. Trinkle et al. [149, 150] proposed a method that employs the NEB method to optimize the MEP for the atomic coordinates and relaxes the cell vectors using Parrinello-Rahman molecular dynamics... 

The analysis of the simulations of crystalline Si 2 has focused on a study of the lattice parameters and their temperatures dependence, on the elastic constants (which can be gotten from the Parrinello-Rahman fluctuation relations [45]), and quantities characterizing the local aspects of the structure (probability distributions to find an atom a distance r away from its equilibrium position, partial radial pair distributions, average bond angles and their distributions, etc.). Of particular interest is also the global order parameter ()) of the phase transition between a-quartz and 5-quartz, which measures the rotation of the (distorted) tetrahedra about the [100] axis,... 

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