Electronic structure of clusters: Applications to high- Tc superconductors

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6071051

Chen, H

A method is presented for studying the electronic structure of clusters by ab initio, self-consistent, local-spin density functional calculations. The linear combination of Gaussian orbitals (LCGO) method was adopted in developing a general cluster program. A variational charge-fitting procedure is used in the evaluation of the matrix elements of the electrostatic potential, and a separate least-squares fitting procedure is used in regard to the exchange-correlation potential. Self-consistent solutions were obtained using this program for the Ba{sub 4}Cu{sub 2}O{sub 7} clusters a portion of the Cu-O chain in the high-{Tc} superconductor YBa{sub 2}Cu{sub 3}O{sub 7}. Four different charge states of Ba{sub 4}Cu{sub 2}O{sub 7} are considered. The spin-polarized calculation predicts zero local moment on Cu sites. The cluster ground state shows strong covalent bonding between the copper and oxygen atoms. Transition-state calculations are made to determine electronic relaxation occurring in photo-emission and to evaluate the Hubbard interaction parameters U{sub dd} and U{sub pp}. We have derived a complete formula to calculate the photo-emission spectrum using the LCGO wave functions. Ultraviolet photoelectron spectra of the YBa{sub 2}Cu{sub 3}O{sub 7} crystal have been calculated. Our results are compared with experiment. Effects of fluorine and nitrogen substitutions to high-{Tc} superconductors are investigated by studying the electronic structure of Ba{sub 4}Cu{sub 2}O{sub 6}N and Ba{sub 4}Cu{sub 2}O{sub 6}F clusters. Results for other interesting systems such as the Fe{sub 2} molecule, the planar CuO{sub 6} and Cu{sub 4}O{sub 4} clusters are also discussed in this work.

• Research Organization: Louisiana State Univ., New Orleans, LA (USA)
• OSTI ID: 6071051
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
ANALYTICAL SOLUTION
BARIUM COMPOUNDS
CHARGE STATES
COPPER COMPOUNDS
CUPRATES
ELECTRONIC STRUCTURE
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POTENTIALS
SOLID CLUSTERS
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
YTTRIUM COMPOUNDS