Numerical Scheme¶

The time-integration scheme is chosen through the numerical_scheme block. Unlike compute_force/species/domain/setup_system, it isn't strictly mandatory: it already defaults to verlet_nve (see Numerical schemes), so a minimal input deck works without touching it at all. Redefine it when you need temperature control.

NVE (default)¶

verlet_nve is a plain velocity-Verlet integrator: energy-conserving, no thermostat. Selecting it explicitly is only ever needed to override a different scheme set elsewhere:

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numerical_scheme: verlet_nve

Langevin NVT (verlet_lnvt)¶

verlet_lnvt runs the same velocity-Verlet steps, with a langevin_thermostat call added into the force computation to couple the system to an implicit heat bath at a target temperature:

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numerical_scheme: verlet_lnvt

langevin_thermostat:
  T: 300 K
  gamma: 0.1 ps^-1

T is the (constant) target temperature and gamma the damping/coupling rate (has a default value, but is always given explicitly with a ps^-1 unit in practice). Instead of a constant T, the target temperature can also ramp linearly over the run with Tstart/Tstop, or follow an arbitrary interpolated profile with tserie/Tserie (a list of times and a matching list of temperatures) — exactly one of the three forms (T, Tstart+Tstop, or tserie+Tserie) must be given.

Combined with the init_temperature_new example from the previous page — which starts the system at 600 K — setting verlet_lnvt with a 300 K target lets the system relax/cool from its initial 600 K towards 300 K over the run.