CASTEP Dynamics task

The CASTEP Dynamics task allows you to simulate how the atoms in a 3D periodic structure will move under the influence of computed forces.

Before performing a CASTEP dynamics calculation you can select the thermodynamic ensemble and associated parameters and define the simulation time, temperature, and pressure.

Selecting the thermodynamic ensemble

Integrating Newton's equations of motion allows you to explore the constant-energy surface (NVE dynamics) of a system. However, most natural phenomena occur under conditions where a system exchanges heat with the environment. These conditions can be simulated using NVT ensembles (either the deterministic Nosé ensemble or the stochastic Langevin ensemble).

External pressure can be incorporated into the dynamics calculation by using either the NPH (constant enthalpy) or the NPT (constant temperature) ensemble.

Defining the time step

An important parameter in the integration algorithm is the time step. To make the best use of the computer time, a large time step should be used. However, if the time step is too large it may lead to instability and inaccuracy in the integration process. Typically, this is manifested as a systematic drift in the constant of motion.

Quantum-mechanical molecular dynamics calculations usually require a smaller time step than forcefield based dynamics applications. However, this is less of an issue in CASTEP because wavefunction and density extrapolation are used.

Constraints during dynamics

CASTEP supports constraints during molecular dynamics simulations. However, you can only apply some of the more basic constraints through the Materials Studio interface:

See Also:

Dynamics
Setting up a molecular dynamics calculation
CASTEP Dynamics dialog