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快乐十分加减乘除618:Optical properties of high-pressure fluid hydrogen across molecular dissociation
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The properties of warm, dense hydrogen are important in material science, plasma physics, planetary science, and astrophysics. We present simulations of its behavior in relation to ongoing, and in some cases controversial, results from static- and dynamic-compression experiments. The optical properties of dense liquid hydrogen are computed under conditions such that hydrogen is changing from a molecular insulating fluid into an atomic metallic fluid. The computed reflectivity and absorption of light agree with recent experimental observations and reconcile the observations with each other, leading to an understanding of this transition, thereby guiding future experimental and theoretical work, as well as being useful for planetary and astrophysical models.
Optical properties of compressed fluid hydrogen in the region where dissociation and metallization is observed are computed by ab initio methods and compared with recent experimental results. We confirm that at T > 3,000 K, both processes are continuous, while at T < 1,500 K, the first-order phase transition is accompanied by a discontinuity of the dc conductivity and the thermal conductivity, while both the reflectivity and absorption coefficient vary rapidly but continuously. Our results support the recent analysis of National Ignition Facility (NIF) experiments [Celliers PM, et al. (2018) Science 361:677–682], which assigned the inception of metallization to pressures where the reflectivity is ～0.3. Our results also support the conclusion that the temperature plateau seen in laser-heated diamond-anvil cell (DAC) experiments at temperatures higher than 1,500 K corresponds to the onset of optical absorption, not to the phase transition.
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Author contributions: M.A.M., D.M.C., and C.P. designed research; G.R., M.A.M., and C.P. performed research; M.A.M. and C.P. contributed new reagents/analytic tools; G.R., M.A.M., D.M.C., and C.P. analyzed data; and M.A.M., D.M.C., and C.P. wrote the paper.
Reviewers: R.J.H., The George Washington University; and R.R., Rostock University, Germany.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1818897116/-/DCSupplemental.
Published under the PNAS license.