FisMat2017 - Submission - View

Abstract's title: Coupled Electron-Ion Monte Carlo study of hydrogen under extreme conditions
Submitting author: Carlo Pierleoni
Affiliation: Maison de la Simulation, CEA-Saclay
Affiliation Address: Maision de la Simulation USR 3441, Batiment 565 - Digiteo, CEA-Saclay, 91191 Gif-sur-Yvette cedex, Francia
Country: France
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: D.M. Ceperley (Phys. Dept., University of Illinois at Urbana-Champaign, USA), M. Holzmann (LPTMC, CNRS and University of Grenoble Alpes, Grenoble, France), M.A. Morales (Physics Division, Lawrence Livermore National Laboratory, USA)

The phase diagram of high pressure hydrogen is of great interest[1]. 

Laboratory experiments are difficult and expensive and ab-initio theory is crucial in developing the field. The accuracy of Density Functional Theory (DFT) calculations is limited and often non-predictive. We present a methodology based on Quantum Monte Carlo to study hydrogen at extreme conditions: the Coupled Electron-Ion Monte Carlo (CEIMC). 


The first application of CEIMC is in computing the principal Hugoniot of deuterium[2]. We find that the maximum compression along the Hugoniot is ~5% higher than with DFT and ~15% higher than most accurate experimental data[3]. 


A second application is to trace the liquid-liquid transition line. A first-order phase transition in the fluid phase between a molecular insulating fluid and a monoatomic metallic fluid has been predicted[4-6]. The existence and precise location of the transition line is relevant for planetary models. Recent experiments reported contrasting results about the location of the transition[7-9]. Theoretical results based on DFT are also very scattered[8]. We report highly accurate CEIMC calculations of this transition finding results that lie between the two experimental predictions, close to that measured in diamond anvil cell experiments but at 25-30 GPa higher pressure. The transition along an isotherm is signaled by a discontinuity in the specific volume, a sudden dissociation of the molecules, a jump in electrical conductivity and loss of electron localization[10]. We discuss the difference observed with respect to the predictions of a different Quantum Monte Carlo method [11].


Finally a third application of CEIMC is to study the stability of the various crystalline molecular phases of hydrogen. We have performed calculations along the T=200K isotherm in the phase III and along the T=414K isotherm in the phase IV. We report a preliminary comparison between CEIMC results and DFT based results and discuss the electronic character of the various phases[12].



[1] J.M. McMahon, M.A. Morales, C. Pierleoni and D.M. Ceperley, Rev. Mod. Phys. 84, 1607 (2012).

[2] N.M. Tubman, E. Liberatore, C. Pierleoni, M. Holzmann and D. M. Ceperley, Phys. Rev. Letts. 115, 045301 (2015).

[3] M. D. Knudson and M. P. Desjarlais, Phys. Rev. Lett. 118, 035501 (2017).

[4] M.A. Morales, C. Pierleoni, E. Schwegler and D.M. Ceperley, PNAS 107, 12799 (2010).

[5] M.A. Morales, J.M. McMahon, C. Pierleoni, D.M. Ceperley, Phys. Rev. Lett. 110, 065702 (2013).

[6] W. Lorenzen, B. Holst, R. Redmer, Phys. Rev. B 82, 195107 (2010).

[7] Zaghoo M, Salamat A, Silvera IF, Phys. Rev. B 93, 155128 (2016)

[8] Ohta K et al. Scientific Reports 5:16560 (2015). 

[9] Knudson MD et al. Science 348, 1455 (2015).

[10] C. Pierleoni, M.A. Morales, G. Rillo, M. Holzmann and D.M. Ceperley, PNAS 113, 4953–4957 (2016).

[11] Mazzola G, Sorella S, Phys Rev Lett 118, 015703 (2017).

[12] G. Rillo et al., in preparation (2017).