3.2 Tight Binding Model

Question 1

How are the electrons modelled in this situation and state the assumption

Answer 1

Localised on the ionic cores

- Assume that they can occasionally hop from atom to atom and they spend nearly all their time bound to the ionic cores

Question 2

Describe how we form the wavefunction for the electron

Answer 2

As a linear combination of atomic orbitals

Question 3

When can we get two bands?

Answer 3

When we have two atoms in the primitive unit cell, or we allow excitation for one atom

Question 4

Describe the band behaviour for a material with two atoms in the primitive unit cell

Answer 4

Expectation is that one band is fully filled

• Does happen at larger separations = INSULATOR
• At smaller separations the bands overlap and we partially fill both by filling the lowest energy states first = METAL