stepper — Generates candidate particle configuration changes by displacing atoms.
stepper ::= (parameter*)
The stepper element holds information about what type of Monte Carlo candidate moves (particle configuration changes) to generate.
none
none
Required, specifies which stepper class to use. Default is ``all'' for the all-particle update (see AllParticleStepper in code documentation). Currently also supports ``single'' (see SingleParticleStepper in code documentation.)
The stepper controls how particle configuration moves should be generated in the Monte Carlo algorithm. Currently, the stepper should always be included within an mcupdate element.
The list of meaningful stepper parameters. n/a indicates not applicable. Note: if center, start_radius, or end_radius is specified, all three must be specified. These are used for preferentially moving atoms in a certain region. If none are specified, no preferential sampling is used.
| name | condition | datatype | default | meaning |
|---|---|---|---|---|
| displacement | Angstroms | scalar | 0.05 | Amount by which to displace each atom. |
| center | n/a | singleParticlePos | none | Spatial position where largest atomic displacements are centered, if using preferential sampling. |
| start_radius | n/a | singleParticlePos | none | The x, y, and z distance from center at which the preferential sampling starts decreasing possible atom displacement. |
| end_radius | n/a | singleParticlePos | none | The x,y, and z distance from center beyond which the preferential sampling does not displace atoms. |
| freeze | correspond to atom index | int | none | The index of an atom. If set, these atoms will not move during the simulation. |
This example shows to how to set up the stepper simulation with some typical options.
<stepper type="all">
<parameter name="displacement">0.014</parameter>
<!-- 'preferential sampling' options. If preferential sampling is not desired, just don't use any of these options -->
<parameter name="center">3.52 4.4 4.4</parameter>
<parameter name="start_radius">4.8 5.7 5.7</parameter>
<parameter name="end_radius">5 6.2 6.2</parameter>
</stepper>