npt_nose_hoover_init

torch_sim.integrators.npt.npt_nose_hoover_init(state, model, *, kT, dt, chain_length=3, chain_steps=2, sy_steps=3, t_tau=None, b_tau=None, seed=None, **kwargs)[source]

Initialize the NPT Nose-Hoover state.

This function initializes a state for NPT molecular dynamics with Nose-Hoover chain thermostats for both temperature and pressure control. It sets up the system with appropriate initial conditions including particle positions, momenta, cell variables, and thermostat chains.

Parameters:

  • model (ModelInterface) – Model to compute forces and energies

  • state (SimState | dict[Literal['positions', 'masses', 'cell', 'pbc', 'atomic_numbers', 'system_idx'], ~torch.Tensor]) – Initial system state as MDState or dict containing positions, masses, cell, and PBC information

  • kT (Tensor) – Target temperature in energy units

  • external_pressure – Target external pressure

  • dt (Tensor) – Integration timestep

  • chain_length (int) – Length of Nose-Hoover chains. Defaults to 3.

  • chain_steps (int) – Chain integration substeps. Defaults to 2.

  • sy_steps (int) – Suzuki-Yoshida integration order. Defaults to 3.

  • t_tau (Tensor | None) – Thermostat relaxation time. Controls how quickly temperature equilibrates. Defaults to 100*dt

  • b_tau (Tensor | None) – Barostat relaxation time. Controls how quickly pressure equilibrates. Defaults to 1000*dt

  • seed (int | None) – Random seed for momenta initialization. Used for reproducible runs

  • **kwargs (Any) – Additional state variables like atomic_numbers or pre-initialized momenta

Returns:

Initialized state containing:

  • Particle positions, momenta, forces

  • Cell position, momentum and mass (all with batch dimensions)

  • Reference cell matrix (with batch dimensions)

  • Thermostat and barostat chain variables

  • System energy

  • Other state variables (masses, PBC, etc.)

Return type:

NPTNoseHooverState

Notes

  • Uses separate Nose-Hoover chains for temperature and pressure control

  • Cell mass is set based on system size and barostat relaxation time

  • Initial momenta are drawn from Maxwell-Boltzmann distribution if not provided

  • Cell dynamics use logarithmic coordinates for volume updates

  • All cell properties are properly initialized with batch dimensions