A quantum Monte Carlo study of the high-pressure phases of solid hydrogen. Ph.D. Thesis

Thesis/Dissertation · Sat Dec 31 04:00:00 EST 1994

OSTI ID:121798

Natoli, V D

Variational and diffusion Monte Carlo are powerful computational methods which can afford accurate estimates of the ground state properties of quantum many-body problems. The authors have applied these Monte Carlo methods to the high pressure phases of solid hydrogen to elucidate those parts of the phase diagram where experimental results are inconclusive or lacking. The method allows them to treat both electrons and protons as quantum particles by incorporating them in the trial wavefunction and avoids the Born-Oppenheimer and harmonic approximations. The authors trial wavefunction uses single-body solutions from a mean-field calculation coupled with standard pair potential terms to achieve the most accurate results to date. Equally accurate results were realized for calculations in the disparate insulating molecular and metallic atomic regime. The authors performed a study of the possible ground state structures of the atomic metallic phase of hydrogen which identifies a new family of low energy atomic structures. Another study was done on the molecular phase over the range of pressures (40-180 GPa) where recent experiments have observed spectral discontinuities and other interesting new phenomena. Particular attention was directed to determining the equation of state and orientational ordering. They find that molecular hydrogen adopts a lower symmetry insulating structure over a wide range of pressure. The results of the atomic and molecular studies are combined to draw conclusions about the molecular-atomic transition and other details about the high pressure phase diagram.

• Research Organization: Illinois Univ., Urbana, IL (United States)
• OSTI ID: 121798
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
EQUATIONS OF STATE
HIGH PRESSURE
HYDROGEN
MONTE CARLO METHOD
PHASE STUDIES
QUANTUM CRYSTALS
SOLIDS