Ab initio cluster study of crystalline NaF
A highly-accurate ab initio cluster model of crystalline NaF has been constructed to explore the limits of cluster methods in the treatment of ionic solids. The focus of this model was the characterization of the lattice environment and its influence on the easily-polarizable fluorine anion. The model consisted of a central all-electron fluorine anion coordinated by pseudopotentials, to represent the nearest-neighbor sodium cations, and a finite array of point charges chosen to generate the correct crystal field from the surrounding infinite ionic lattice. The wavefunction and properties of the anion were calculated using the restricted Hartree-Fock and configuration interaction techniques from quantum chemistry. An extensive analysis of basis set incompleteness errors in the anion wavefunction was performed. Important features were identified in the embedded anion, such as its distortion under the influence of the lattice compressions, its stabilization from the Madelung potential, and its changes in size due to electron correlations. Bulk properties of the rocksalt-structure (B1) NaF crystal were derived from the total mode energies, calculated as a function of the crystal volume. The properties included the zero-pressure lattice constant, cohesive energy, and bulk modulus, and the pressure-volume equation-of-state. A series of test calculations explored the relationships, and their underlying physical mechanisms, between the features of the embedded anion and the bulk properties of the crystal. These features often produced opposing changes in the properties, demonstrating the importance of a thorough and systematic treatment of the embedded anion. The most thorough test calculation gave bulk properties that were within 1% of experiment. Using an embedded anion model for the high-pressure cesium-chloride (B2) phase of NaF, the B1-to-B2 structural transition was correctly predicted at 25 GPa, in excellent agreement with the experimental values of 23 to 27 GPa.
- Research Organization:
- California Univ., Davis, CA (United States)
- OSTI ID:
- 7295965
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Pressure effect on elastic, lattice dynamic and superconducting behaviour of yttrium sulfide: A first principle study
High pressure phase transformation in yttrium sulfide(YS): A first principle study
Related Subjects
SODIUM FLUORIDES
CRYSTAL MODELS
CONFIGURATION INTERACTION
CRYSTAL LATTICES
HARTREE-FOCK METHOD
IONIC CRYSTALS
ALKALI METAL COMPOUNDS
CALCULATION METHODS
CRYSTAL STRUCTURE
CRYSTALS
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
MATHEMATICAL MODELS
SODIUM COMPOUNDS
664000* - Atomic & Molecular Physics- (1992-)