Random kick

In stochastical methods the random kick is typically somewhat larger, and a standard minimization is carried out starting at the perturbed geometry. This may or may not produce a new minimum. A new perturbed geometry is then generated and minimized etc. There are several variations on how this is done. 

To include the effects of collisions on the rotational motion part of any of the above C(t) functions, one must introduce a model for how such collisions change the dipole-related vectors that enter into C(t). The most elementary model used to address collisions applies to gaseous samples which are assumed to undergo unhindered rotational motion until struck by another molecule at which time a randomizing "kick" is applied to the dipole vector and after which the molecule returns to its unhindered rotational movement. 

The most commonly used stochastic methods are the torsional Monte Carlo method11101 and the cartesian stochastic (or random kick) method11111. The two methods differ in the coordinate system in which they operate. The torsional Monte Carlo method uses internal coordinates, while the random kick method uses cartesian coordinates. The advantage of using internal coordinates is that the molecular degrees of freedom are reduced. The reason for choosing torsional angles as the vari-... 

Conformational isomers represent minima on an energy surface, and all structures and the corresponding strain energies can be obtained by a careful analysis. This can be performed manually (such as in Sections 17.3 and 17.4) or automatically. An automatic procedure may involve a systematic search (grid search methods), a stochastic search (e.g., torsional Monte Carlo or cartesian stochastic, i.e., the random kick method) or molecular dynamics (see Chapter 5 and Section 16.5). Implemented in MOMEC is a random kick stochastic search module, and this has been shown to lead to excellent results, not only for conformational equilibria, but also for distributions of configurational isomers[37]. 

In this section we will use the random kick module to search for conformers of the complex [Co(en)3]3+. 

Under Execute select Random Kick. Select Kick atoms selected in HyperChem and set the other parameters to the values shown in Fig. 17.5.1. 

In stochastical methods the random kick is typically somewhat laraer. and a standard ... 

These methods starts from a given geometry, which typically is a (local) minimum, and new configurations are generated by adding a random kick to one or more atoms. In Monte Carlo (MC) methods the new geometry is accepted as a starting point for the next... 

There are two major techniques for generating an ensemble Monte Carlo and Molecular Dynamics. In Monte Carlo (MC) methods a sequence of points in phase space is generated from an initial geometry by adding a random kick to the... 

The physics behind this relation is the fluctuation-dissipation theorem the same random kicks of the surrounding molecules cause both Brownian diffusion and the viscous dissipation leading to the frictional force. It is -instructive to calculate the time scale t required for the particle to move a... 

Open the molecule-add-restraint tab in the project tab and add the atoms that should not be subjected to the random kick procedure, that is, select all atoms except both carbon atoms and all eight hydrogen atoms of each of the three ligands. Alternatively, you can restrain the atoms to be kicked and then invert the restraints. 

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