First-principles study of the hydrogen-metal system

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:106825

Wang, Yan

The ab initio pseudopotential method within the local-density-functional formalism with a plane-wave basis is implemented to study the properties of hydrogen in yttrium. With a soft pseudopotential scheme, satisfactory convergence is achieved with an energy cutoff of 30-40 Ry. A correction in the exchange-correlation functional is needed to handle the outer core contribution in this early transition metal. The calculated structural properties of bulk yttrium are in good agreement with experiments. In the solid solution phase of hydrogen in hexagonal close-packed yttrium ({alpha}-YH{sub x}, x < 0.5), the occupation of the tetrahedral site is found to be energetically favorable. The calculated vibrational frequency in a one-dimensional double-well potential along the c axis and the diffusion barrier from one tetrahedral site to the neighboring octahedral site are in excellent agreement. The pairing of hydrogen across a metal atom is energetically favorable, which is explained from the electronic structure of the system. The study of {beta}-YH{sub 2+z} is carried out with the metal atoms forming a face-centered cubic lattice and with 0 {<=} x {<=} 1. The total energy, electronic and structural properties, density of states (DOS), angular-momentum-decomposed DOS, and charge transfer are investigated by the supercell modeling method. Volume contraction with increasing x and the (420)-plane ordering of hydrogen are studied. Yttrium trihydride with the metal atoms in the hexagonal close-packed (HCP) structure is examined. The hexagonal YH{sub 3} with wave-like hydrogen displacements is energetically more stable than the cubic structure, and is consistent with the neutron diffraction data for YD{sub 3} and HoD{sub 3}. These hydrogen displacements are found to be Peierls-like distortions. The calculated final LDA band structure for YH{sub 3} yields a semimetal rather than a semiconductor. The existence of excitonic insulating ground state is speculated.

• Research Organization: Georgia Inst. of Tech., Atlanta, GA (United States)
• OSTI ID: 106825
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ANALYTICAL SOLUTION
BAND THEORY
CRYSTAL LATTICES
DEUTERIUM
ELECTRONIC STRUCTURE
HYDROGEN
MATHEMATICAL MODELS
VIBRATIONAL STATES
YTTRIUM
YTTRIUM HYDRIDES