Bayesian Calibration of Force-fields
from Experimental Data: TIP4P Water

Molecular dynamics (MD) simulations give access to equilibrium structures and dynamic properties given an ergodic sampling and a force-field accuracy. The force-field parameters are calibrated to reproduce properties measured by experiments or simulations. The main contribution of this paper is an approximate Bayesian framework for the calibration of the force-field parameters and for their uncertainty quantification, without assuming parameter uncertainty to be Gaussian. To this aim, since the likelihood function of the MD simulation models are intractable in absence of Gaussianity assumption, we use a likelihood-free inference scheme known as approximate Bayesian computation (ABC) and propose an adaptive population Monte Carlo ABC algorithm, which is illustrated to converge faster and scales better than previously used ABCsubsim algorithm for calibration of force-field of a helium system.

The second contribution is the adaption of ABC algorithms for High Performance Computing to MD simulation within the Python ecosystem ABCpy. This adaptation includes a novel use of dynamic allocation scheme for MPI. We illustrate the performance of the developed methodology to learn posterior distribution and Bayesian estimates of Lennard-Jones force- field parameters of helium and TIP4P system of water implemented both for simulated and experimental datasets collected using Neutron and X-ray diffraction. For simulated data, the Bayesian estimate is in close agreement with the true parameter value used to generate the dataset. For experimental as well as for simulated data, the Bayesian posterior distribution shows a strong correlation pattern between the force-field parameters. Providing an estimate of the entire posterior distribution, our methodology also allows us to perform uncertainty quantification of model prediction. This research opens up the possibility to rigorously calibrate force-fields from available experimental datasets of any structural and dynamic property

Antonietta Mira