ensemble — A method to propagate a particle set.
ensemble ::= (parameter*)
The ensemble element contains parameters defining the external properties of a particle system, such as an external temperature or pressure, and control parameters for a propagator.
Create a propagator to move a particle set and set the initial conditions according to the external parameters.
The following elements occur in simulation: parameter
Required, the name of the ensemble.
Optional, the numerical algorithm to intergate equations of motion.
Optional, external constraints applied to the particle.
Optional, the particle set to be propagated.
Reserved.
The common parameters to set the external physical quantities are:
| name | condition | datatype | ensenble | meaning |
|---|---|---|---|---|
| temperature | K | scalar | all | Set the initial and external temperature. |
| timestep | fsec | scalar | all | Set the time step for the numrical integrator. |
| clock | fsec | scalar | all | Set the MD clock. An output file contains the MD clock at the end of a run. |
| friction | fsec-1 | scalar | evn | tvn | Set the friction coefficient. For <ensemble name="evn"/>, the friction parameter is a damping parameter and its effect is equivalent to choosing <ensemble name="sdmin"/>. |
| pressure | kB | scalar | all | Set the external pressure. |
The list of names meaningful to ensemble for ohmms and related applications.
| name | method | meaning |
|---|---|---|
| static | none | force | Calculate the total energy. Calculate force, if method="force". |
| evn | velocity-verlet | verlet | Perform constant energy, volume and number simulation using either velocity-verlet (default) or verlet. |
| tvn | langevin | nose-hoover | Perform constant temperature, volume and number simulation using Langevin or Nose-Hoover heat bath. |
| cgmin | NA | Structural minimization by the conjugate-gradient method. |
| sdmin | NA | Structural minimization by the steepest-descent method. |
| phonon | NA | Frozen-phonon calculations. |
This example shows how to set the ensemble to perform a constant TemperatureVolumeNumber simulation at a temperature 500 K with a time step 2 fsec and a friction coefficient of 0.5 fsec-1.
<ensemble name="tvn" method="langevin">
<parameter name="temperature" condition="K"> 500 </parameter>
<parameter name="friction" condition="fsec-1"> 0.5 </parameter>
<parameter name="timestep" condition="fsec"> 2 </parameter>
</ensemble>