Simulating Raman Spectra using molecular dynamics, and identification of\n high-pressure phases III and IV in hydrogen

2013/02/22 by Ioan-Bogdan Magdău, Magdau, Ioan B., Graeme J. Ackland +1
Earth and Planetary Sciences · Physics and Astronomy · #Advanced Chemical Physics Studies #FOS: Physical sciences #High-pressure geophysics and materials #Materials Science (cond-mat.mtrl-sci) #Quantum, superfluid, helium dynamics

paper · pdf · doi:10.48550/arxiv.1302.5581

openalex publication_date 2013/02/22 · openalex created_date 2022/09/30 · openalex updated_date 2026/07/28

Abstract

We present a technique for extracting Raman intensities from ab initio\nmolecular dynamics (MD) simulations at high temperature. The method is applied\nto the highly anharmonic case of dense hydrogen up to 500 K for pressures\nranging from 180 GPa to 300 GPa. On heating or pressurizing we find first-order\nphase transitions at the experimental conditions of the phase III - IV\nboundary. Direct comparison of Raman vibrons with experiment provides excellent\ndiscrimination between subtly different structures, found in MD. We find\ncandidate structures whose Raman spectra are in good agreement with experiment.\nThe new phase obtained in high temperature simulations adopts a dynamic, simple\nhexagonal structure with three layer types: freely rotating hydrogen molecules,\nstatic hexagonal trimers and rotating hexagonal trimers. We show that\npreviously calculated structures for phase IV are inconsistent with experiment,\nand their appearance in simulation is due to finite size effects.\n

Related

• Experimental phase transition mapping for hydrogen above 300 K up to 300 GPa
• Low temperature phase diagram of hydrogen at pressures up to 380 GPa. A possible metallic phase at 360 GPa and 200 K
• Charge density wave in hydrogen at high pressure
• Nuclear Quantum Effects Induce Metallization of Dense Solid Molecular Hydrogen
• Raman spectra of hydrocarbons under extreme conditions of pressure and temperature: a first-principles study