Module: opes

Description	Usage
On-the-fly Probability Enhanced Sampling (OPES)
Authors: Michele Invernizzi

Details

The OPES module contains the implementation of the on-the-fly probability enhanced sampling mehtod (OPES).

The OPES method aims at sampling a given target distribution over the configuration space, $p^{\text{tg}}(\mathbf{x})$, different from the equilibrium Boltzmann distribution, $P(\mathbf{x})\propto e^{-\beta U(\mathbf{x})}$. To do so, it incrementally builds a bias potential $V(\mathbf{x})$, by estimating on-the-fly the needed probability distributions:

$$V(\mathbf{x}) = -\frac{1}{\beta}\log\frac{p^{\text{tg}}(\mathbf{x})}{P(\mathbf{x})}\, .$$

The bias quickly becomes quasi-static and the desired properties, such as the free energy, can be calculated with a simple reweighting REWEIGHT_BIAS.

Depending on the kind of target distribution one wishes to sample, different the various biases listed in the table below can be used.

Installation

This module is not installed by default. Add --enable-modules=opes to your './configure' command when building PLUMED to enable these features.

Usage

The OPES module contains three bias actions, OPES_METAD and OPES_METAD_EXPLORE that sample metadynamics-like target distributions (e.g. the well-tempered one), and OPES_EXPANDED that samples expanded ensembles target distributions (replica-exchange-like). It also contains various expansion collective variables (ECVs) to define such expanded targets. These expansion collective variables (ECVs) are used to define the expanded ensemble to be sampled by OPES_EXPANDED as discussed in the papers cited below. ECVs take some underlying colvar as argument and have as output components the same colvars.

Actions

The following actions are part of this module

Tags

BIAS OPES_EXPANSION_CV

BIAS: bias potentials that can be used to force rare events to occur in MD simulations OPES_EXPANSION_CV: expansion cvs that can be used with the OPES method

Name	Description	Tags
ECV_CUSTOM	Use some given CVs as a set of expansion collective variables (ECVs).	OPES_EXPANSION_CV
ECV_LINEAR	Linear expansion, according to a parameter lambda.	OPES_EXPANSION_CV
ECV_MULTITHERMAL	Expand a simulation to sample multiple temperatures simultaneously.	OPES_EXPANSION_CV
ECV_MULTITHERMAL_MULTIBARIC	Expand a simulation to sample multiple temperatures and pressures.	OPES_EXPANSION_CV
ECV_UMBRELLAS_FILE	Target a multiumbrella ensemble, by combining systems each with a parabolic bias potential at a different location.	OPES_EXPANSION_CV
ECV_UMBRELLAS_LINE	Target a multiumbrella ensemble, by combining systems each with a parabolic bias potential at a different location.	OPES_EXPANSION_CV
OPES_EXPANDED	On-the-fly probability enhanced sampling with expanded ensembles for the target distribution.	BIAS
OPES_METAD	On-the-fly probability enhanced sampling with metadynamics-like target distribution.	BIAS
OPES_METAD_EXPLORE	On-the-fly probability enhanced sampling with well-tempered target distribution in exploreation mode.	BIAS

References

More information about this module is available in the following articles:

• M. Invernizzi, M. Parrinello, Rethinking Metadynamics: From Bias Potentials to Probability Distributions. The Journal of Physical Chemistry Letters. 11, 2731–2736 (2020)
• M. Invernizzi, P. M. Piaggi, M. Parrinello, Unified Approach to Enhanced Sampling. Physical Review X. 10 (2020)
• M. Invernizzi, M. Parrinello, Exploration vs Convergence Speed in Adaptive-Bias Enhanced Sampling. Journal of Chemical Theory and Computation. 18, 3988–3996 (2022)