Learning the exchange-correlation functional from nature with fully differentiable density functional theory

Physical Review Letters American Physical Society 127 (2021) 126403

Authors:

Muhammad F Kasim, Sam M Vinko

Abstract:

Improving the predictive capability of molecular properties in ab initio simulations is essential for advanced material discovery. Despite recent progress making use of machine learning, utilizing deep neural networks to improve quantum chemistry modeling remains severely limited by the scarcity and heterogeneity of appropriate experimental data. Here we show how training a neural network to replace the exchange-correlation functional within a fully differentiable three-dimensional Kohn-Sham density functional theory framework can greatly improve simulation accuracy. Using only eight experimental data points on diatomic molecules, our trained exchange-correlation networks enable improved prediction accuracy of atomization energies across a collection of 104 molecules containing new bonds, and atoms, that are not present in the training dataset.

Excited-state potentials for modelling dense plasmas from first principles

Plasma Physics and Controlled Fusion IOP Publishing (2021)

Authors:

Patrick James Hollebon, Justin S Wark, Sam Vinko

Abstract:

The modelling of dense plasmas using finite-temperature density functional theory has proven very successful in determining transport properties and the equation of state of systems where quantum many-body effects and correlations play a key role in their structure. Here we show how excited-state projector augmented-wave potentials can be used to extend these calculations to explicitly model core-hole states, allowing for the calculation of the electronic structure of a range of integer charge configurations embedded in a dense plasma environment. Our excited-state potentials show good agreement with all-electron calculations at finite-temperatures, motivating their use as an efficient approach in modelling from first principles both the structure of strongly-coupled non-equilibrium plasmas and their interaction with intense X-rays.

Astronomy Domine: advancing science with a burning plasma

Contemporary Physics Taylor and Francis (2021)

Authors:

steven Rose, Peter Hatfield

Abstract:

Inertial Confinement Fusion (ICF) is a subject that has been studied for decades, because of its potential for clean energy generation. Although thermonuclear fusion has been achieved, the energy out has always been considerably less than the energy in, so high energy gain with a burning thermonuclear plasma is still some way off. A multitude of new science has come from the ICF programme that is relevant outside the field (typically in astrophysics). What we look at in this text is what new science can come from the much more extreme conditions that would be created in the laboratory if a burning ICF plasma could be created -- in terms of energy density the most extreme macroscopic environment ever created. We show that this could impact science from particle physics through astrophysics and on to cosmology. We also believe that the experiments that we propose here are only a small part of the science that will be opened up when a burning thermonuclear plasma is created in the laboratory.

An investigation of efficient muon production for use in muon catalyzed fusion

Journal of Physics: Energy IOP Publishing 3:3 (2021) 035003-035003

Authors:

R Spencer Kelly, Lucy JF Hart, Steven J Rose

Generating ultradense pair beams using 400 GeV/c protons

Physical Review Research American Physical Society 3 (2021) 023103

Authors:

CD Arrowsmith, N Shukla, N Charitonidis, R Boni, H Chen, T Davenne, Anthony Dyson, Dh Froula, JT Gudmundsson, Brian Huffman, Y Kadi, B Reville, S Richardson, S Sarkar, Jl Shaw, Lo Silva, P Simon, Rmgm Trines, R Bingham, G Gregori

Abstract:

An experimental scheme is presented for generating low-divergence, ultradense, relativistic, electron-positron beams using 400 GeV/c protons available at facilities such as HiRadMat and AWAKE at CERN. Preliminary Monte Carlo and particle-in-cell simulations demonstrate the possibility of generating beams containing 1013–1014 electron-positron pairs at sufficiently high densities to drive collisionless beam-plasma instabilities, which are expected to play an important role in magnetic field generation and the related radiation signatures of relativistic astrophysical phenomena. The pair beams are quasineutral, with size exceeding several skin depths in all dimensions, allowing the examination of the effect of competition between transverse and longitudinal instability modes on the growth of magnetic fields. Furthermore, the presented scheme allows for the possibility of controlling the relative density of hadrons to electron-positron pairs in the beam, making it possible to explore the parameter spaces for different astrophysical environments.