I. Molecular simulations of buckyball fullerenes. II. Quantum chemistry studies of high-[Tc] superconductors

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:5604246

Guo, Y

To interpret and predict the unusual chemical and physical properties of the C[sub 60] and related fullerenes, fullerites, and molecular/solid state derivatives, the author started with the graphite force field (GraFF) developed for sp[sup 2] carbon centers (based on fitting experimental lattice parameters, elastic constants, phonon frequencies for graphite and alkali-intercalated graphite), and successfully predicted vibrational frequencies, fullerite and alkali-doped fullerite crystal structure, density, heat of sublimation, and compressibility, etc., for C[sub 60], C[sub 70] and their derivatives. He developed a highly accurate force field for C[sub 60] in agreement with all 14 experimental frequencies within abs error 3.0 cm[sup [minus]1]. He develops the GVB superexchange CI (GVB-X-CI) method to study the superexchange coupling interaction of high-[Tc] materials. The J[sub dd] can be calculated from the first principle at about the same accuracy as experiment. The results indicate the superconductivity in Cu-O plane of these cuprates arise from a essentially magnetically induced interaction, that is, (i) all Cu have a Cu[sup II] d[sup 9] oxidation state with one unpaired spin that is coupled antiferromagnetically to the spins of adjacent Cu[sup II] sites; (ii) reduction below the cupric Cu[sup II] state leads to Cu[sup I] d[sup 10] sites with a highly mobile Cu(3d) electron, and these extra electrons hop from site to site. The hopping of these extra electrons causes the flipping of the local spin moment of the antiferromagnetic background; (iii) oxidation beyond the cupric Cu[sup II] state leads not to Cu[sup III] but to oxidized oxygen atoms with an highly mobile Op hole, which is ferromagnetically coupled to the adjacent Cu[sup II] d electrons despite the fact that this is opposed by the direct dd exchange. This coupling induces an attractive interaction between conduction electrons that is responsible for the superconductivity.

• Research Organization: California Inst. of Tech., Pasadena, CA (United States)
• OSTI ID: 5604246
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
FULLERENES
PHYSICAL PROPERTIES
SUPERCONDUCTIVITY
MOLECULAR CLUSTERS
PREDICTION EQUATIONS
ACCURACY
COMPRESSIBILITY
CRYSTAL STRUCTURE
CUPRATES
DENSITY
HIGH-TC SUPERCONDUCTORS
LATTICE PARAMETERS
PHYSICAL CHEMISTRY
SIMULATION
SUBLIMATION
CARBON
CHEMISTRY
COPPER COMPOUNDS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
EQUATIONS
EVAPORATION
MECHANICAL PROPERTIES
NONMETALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
360607* - Other Materials- Superconducting Properties- (1992-)
665411 - Basic Superconductivity Studies- (1992-)
360606 - Other Materials- Physical Properties- (1992-)