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Phys 460 Lecture 6

( pdf version - 6 slides/page )
Wednesday, September 13, 2006
Lecturer: Richard Martin 		Homework 3

Reading:
Kittel, Chapt. 3

Binding of Crystals
Outline

  1. From last times:
    • Typical Crystal Structures
    • Diffraction, Fourier Analysis, and the Reciprocal Lattice
  2. What makes crystals bind?
    • Electronic states change as nuclei come together
    • Quantum Effect - cannot be undertood in classical physics
    • We will consider simple versions of quantum effects at this stage - more later
  3. Types of Binding
    • Van der Waals
    • Ionic
    • Metallic
    • Covalent
    • (Hydrogen)
  4. Van der Waals - very weak binding
    • Due to quantum fluctuations and Coulomb interaction)
    • Leads to 1/r6 attraction
    • Strong repulsion at short distance due to exclusion principle
    • Typically close packed crystals
  5. Ionic - strong binding
    • Must pay cost of making ions
    • Ions interact as +-1/R
    • Madelung constant - difficult to calculate
    • Simple two atom per cell structures like NaCl, CsCl
  6. Metals - strong binding
    • Electrons change and delocalize
    • Discussed more later
    • Typically close packed crystals
  7. Covalent - strongest binding
    • Form chemical bonds
    • Simple interpretaion as bonmds but difficult to calculate
    • Open, directional structures such as diamond structure
Email question/comments/corrections to rmartin@uiuc.edu