Two-band model for halogen-bridged mixed-valence transition-metal complexes. I. Ground state and excitation spectrum

Journal Article · Sat Mar 14 23:00:00 EST 1992 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.45.6408· OSTI ID:7047472

Gammel, J T; Saxena, A; Batistic, I; Bishop, A R ^[1]; Phillpot, S R ^[2]

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1. Centers for Materials Science and Nonlinear Studies and Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

We consider a 3/4-filled, two-band discrete tight-binding Peierls-Hubbard model for an isolated chain of a halogen-bridged, mixed-valence, transition-metal linear-chain complex (HMMC or {ital MX} chain). We have employed the adiabatic approximation in which the quantum fluctuations associated with phonons are implicitly treated as an external field for the electrons, and treat electron-electron effects in the Hartree-Fock approximation. We investigate ground states as functions of the model parameters and doping-induced and photoinduced excitations---kinks, polarons, bipolarons, and excitons. Results for several experimental observables, including the lattice distortion, the excess charge and spin densities of defects, and the optical absorption, are compiled. For the ground state, we find that the bond-order-wave (BOW) portion of the one-band phase diagram is eliminated from the two-band phase diagram, in agreement with the lack of real materials in the pure BOW phase. The extent of electron-hole asymmetry and of spatial localization or delocalization of defects is explored. Two separate solitons or polarons are compared with corresponding bipolarons. We demonstrate explicitly the need to employ the two-band model for a realistic modeling of the {ital MX} systems, focusing on three specific systems: (a) highly distorted, valence-localized (strongly charge-disproportionated) PtCl, (b) moderately distorted PtBr, and (c) weakly distorted, valence-delocalized (weak charge-density wave) PtI. The compilation of results reported here constitutes a reference resource against which the rapidly expanding experimental data can be compared.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 7047472
• Journal Information: Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 45:12; ISSN 0163-1829; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

665000* -- Physics of Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BORIDES
BORON COMPOUNDS
CHLORIDES
CHLORINE COMPOUNDS
COLLECTIVE EXCITATIONS
COMPLEXES
ELECTRON-ELECTRON INTERACTIONS
ELECTRONIC STRUCTURE
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUCTUATIONS
GROUND STATES
HALIDES
HALOGEN COMPOUNDS
HARTREE-FOCK METHOD
INTERACTIONS
IODIDES
IODINE COMPOUNDS
LEPTON-LEPTON INTERACTIONS
PARTICLE INTERACTIONS
PHONONS
PLATINUM CHLORIDES
PLATINUM COMPOUNDS
QUASI PARTICLES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
VARIATIONS