Nuclear quantum effects¶

Most atomistic simulations treat nuclei as classical particles, that sample a Boltzmann distribution. This approximation breaks down for light nuclei (hydrogen above all) and high-frequency vibrations, requiring more sophisticated statistical sampling to compute accurate statistical and dynamical properties.

Path integral molecular dynamics

This example shows how to run a path integral molecular dynamics simulation using i-PI, analyze the output and visualize the trajectory in chemiscope. It uses LAMMPS as the driver to simulate the q-TIP4P/f water model.

Path integral molecular dynamics

Path integral metadynamics

This example shows how to run a free-energy sampling calculation that combines path integral molecular dynamics to model nuclear quantum effects and metadynamics to accelerate sampling of the high-free-energy regions.

Path integral metadynamics

Quantum heat capacity of water

This example shows how to estimate the heat capacity of liquid water from a path integral molecular dynamics simulation. The dynamics are run with i-PI, and LAMMPS is used as the driver to simulate the q-TIP4P/f water model.

Quantum heat capacity of water

Multiple time stepping and ring-polymer contraction

This notebook provides an introduction to multiple time stepping and ring polymer contraction, two closely-related techniques, that are geared towards reducing the cost of calculations by separating slowly-varying (and computationally-expensive) components of the potential energy from the fast-varying (and hopefully cheaper) ones.

Multiple time stepping and ring-polymer contraction