NQEAIMD

Fast and accurate simulation of nuclear quantum effects in ab-initio molecular dynamics by a generalized Langevin equation

 Partecipanti

Mappa

 Word cloud

Esplora la "nuvola delle parole (Word Cloud) per avere un'idea di massima del progetto.

 Obiettivo del progetto (Objective)

'Computer simulations of matter at the atomic level provide insights complementary to experiments in a number of different physical, chemical and biological problems. The quantum nature of nuclei is usually disregarded, because of the computational burden inherent in an accurate treatment. However, these nuclear quantum effects have important, qualitative consequences, in particular when light atoms such as hydrogen are present. Moreover, inelastic neutron scattering techniques have been developed in the past years, which probe experimentally the quantum distribution of proton velocities, and would benefit from the availability of inexpensive modeling tools. Here we propose the development of a new methodology for treating nuclear quantum effects, which reduces computational effort without sacrificing accuracy by combining in a unified formalism path integral molecular dynamics and the 'quantum thermostat', based on correlated-noise stochastic equations. We expect in this way to be able to treat routinely nuclear quantum effects together with an accurate, first-principles evaluation of inter-atomic forces, while so far this has only been attempted occasionally and with great computational effort. These theoretical developments will be accompanied by applications to problems of fundamental and technological relevance. After having demonstrated the reliability of our approach on a few simple, controlled examples, we will tackle the problem of ab-initio water, in particular with reference to recent inelastic neutron scattering experiments performed at ISIS. At a later stage we will choose a more complex problem to demonstrate our approach. Among the possible applications, hydrogen-storage materials are particularly promising, also considering the opportunity of a collaboration with the experimental group of Prof. Bill David, who has been performing leading-edge experiments on complex hydrides in the past few years at the Rutherford Appleton Laboratories in Oxfordshire.'

Introduzione (Teaser)

The simultaneous simulation of nuclear quantum effects both for electrons and light nuclei is now considerably less expensive, thanks to an EU project. This development will help to improve materials used in lithium batteries, fuel cells, and many other chemical and biological applications.

Descrizione progetto (Article)

At the quantum level, materials behave in a way that is substantially different to that in the everyday, Newtonian world.

This can affect the manner in materials and devices that contain hydrogen or other light atoms function.

Computer-based simulation techniques are used to model this behaviour.For condensed-phase systems, density functional theory (DFT) provides an acceptably accurate framework for looking at the quantum electronic structure.

DFT is, however, costly.

Combining DFT simulations with path integral molecular dynamics (PIMD), which is a convenient approach to deviations from Newtonian behaviour, is desirable in certain cases.

The problem is that using the two together is both highly expensive and time-consuming.The 'Fast and accurate simulation of nuclear quantum effects in ab-initio molecular dynamics by a generalised Langevin equation' (NQEAIMD) project aimed to make PIMD simulations less costly.

This was to facilitate a combination of nuclear quantum effects (NQEs) with DFT simulations.The researchers began by applying a coloured-noise, Generalised Langevin Equation (GLE) to a PIMD simulation.

When they had established this methodology, they studied the impact of NQEs on the properties of water.

Then they extended it to more complex problems in collaboration with experimental groups.The team developed a hybrid technique called PI+GLE, which reduces the cost to one-fifth or less. PI+GLE was then improved to produce the PIGLET method, which could make it a routine matter to include NQEs in ab-initio molecular dynamics.

To this end, the researchers also developed i-PI, an interface using electronic structure codes, and released it as open-source code. The results of NQEAIMD will have an impact on computer simulation work by other scientists. Simulations should be more accurate in the case of materials and chemicals that contain light atoms, including hydrogen.

In turn, this could help the fulfilment of the potential of computer aided materials design, leading to better batteries, enzymes, fuel cells and other devices