Chapter 4: MD Example

Question 1

MD Interactions

Answer 1

• short-range repulsion: Pauli exclusion principle
• mid-range attraction: dispersion
• long-range: electrostatics

Question 2

Lennard-Jones Potential

Answer 2

• one of simplest ways to capture short- and mid-range interactions

Question 3

Lennard-Jones Potential

(Graph)

Answer 3

• min{V_LJ(r)} = V_LJ(2^1/6) = -ε

Question 4

Lennard-Jones Potential

(Cut-off Distance)

Answer 4

• cannot do infinite integral → introduce cut-off distance r_c
  
  • typically r_c = 2.5σ
  • use to shift potential so that V_LJ(r>|r_c) = 0

Question 5

Simulation Units

Answer 5

• reduced (dimensionless) units are useful → no rounding errors
• For mechanical systen, need three independent units
  
  • e.g. mass, energy, length
    
    • addition of electrostatics requires fundamental charge e_o

Question 6

Law of Corresponding States

Answer 6

Using reduced units allows simulation of a class of systems, rather than specific example-systems