PHYS4031 Statistical Mechanics
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PHYS4031 Statistical Mechanics
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Front Matter
  • Front Matter - Assessment Scheme, Academic honesty, TAs, Tips for learning Stat Mech, and Assignment Policy
  • Course Learning Outcomes
  • Time Table and TA consultation hours
  • Reference book list and books reserved in University Library


  • Lecture Notes
  • Chapter 1 - What is statistical mechanics and why we need it? Coverage of our course and learning outcomes
  • Chapter 1 Appendix - Brief history and some big names
  • Class work in Week 1 - Uniform spatial distribution of molecules
  • Class work in Week 1 - Key Results
  • Class work in Week 1 Appendix A - Gaussian distribution function
  • Class work in Week 1 - Extension (Optional) - Central Limit Theorem
  • Chapter 2 - Short review on essential thermodynamics
  • Chapter 2 Appendix A - Natural variables of thermodynamic functions
  • Chapter 2 Appendix B - Legendre transformation and its graphical interpretation
  • Chapter 3 Part 1 - Macrostate, Accessible Microstates and distributions in isolated system, Postulate of Equal a priori probabilities
  • Chapter 3 Part 2 - Microcanonical Ensemble, Time average versus ensemble average, properly choosing members of an ensemble
  • Chapter 3 Part 3 - Boltzmann's formula S = k ln W and what is W, the most probable distribution
  • Chapter 3 Appendices A and B - Phase space (Gamma-space and mu-space), Stirling formula for ln N!
  • Chapter 4 Part 1 - Physics and applications of S=k ln W - The formula makes sense, irreversible processes and arrow of time
  • Chapter 4 Part 2 - Two systems in contact and thermodynamic results, S=k ln W re-interpreted as an average over ensemble members, Gibbs entropy formula
  • Chapter 4 Appendix A - Schottky Defects in solids and related problems
  • Chapter 4 Appendix B - Classical Ideal Gas (Microcanonical Ensemble)
  • Chapter 4 Appendices C and D - Volume of D-dimensional Sphere and a List of standard problems
  • Chapter 4 Appendix E (Optional) - Entropy of classical ideal gas entirely based on thermodynamics
  • Chapter 4 Appendix F - What is W in N-particle quantum systems and What are single-particle states?
  • Chapter 5 Part 1 - System in thermal equilibrium with a heat bath - Defining the problem, the Boltzmann Distribution and the Partition Function Z(T,V,N)
  • Chapter 5 Part 2 - The Partition Function, Connecting Z to thermodynamic quantities, Canonical Ensemble - Concepts
  • Chapter 5 Appendix (Optional) - Gaussian form of probability of finding system at energy E near the most probable value
  • Chapter 6 Part 1 - Statistical Physics of Typical Systems (Canonical Ensemble) - Two-level systems (General treatment)
  • Chapter 6 Part 2 - Paramagnetism (Essential Background on magnetism, J=1/2 as special case of two-level systems, General J case and Brillouin functions)
  • Chapter 6 Part 3 - Classical (Langevin) theory of paramagnetism (ignoring quantization of z-component of magnetic moments)
  • Chapter 6 Part 4 - Statistical physics of harmonic oscillators and heat capacity of solids
  • Chapter 6 Part 5 - Statistical physics of vibrational and rotational motions in molecules
  • Chapter 6 Part 6 - Ideal quantum gases within canonical ensemble (formalism, difficulties and way out)
  • Chapter 7 Part 1 - Fermi-Dirac and Bose-Einstein distributions as the most probable distributions
  • Chapter 7 Part 2 - Maxwell-Boltzmann distribution for classical particles as a by-product
  • Chapter 7 Part 3 - Key results and summary on the most probable distribution approach
  • Chapter 7 Appendix (Optional) - Re-deriving Boltzmann distribution and Partition Function using Lagrange Multipliers method
  • Chapter 8 - Density of single-particle states (General Approach)
  • Chapter 9 Part 1 - Classical Statistical Mechanics and standard applications
  • Chapter 9 Part 2 - Nonideal gases (Phenomena - Phase diagram, Real gases, Interactions)
  • Chapter 9 Part 3 - Non-ideal classical gas (Partition function and second virial coefficient) [lead sheet]
  • Chapter 9 Part 3 - Non-ideal classical gas (second virial coefficient, van der Waals equation of state)
  • Chapter 9 Part 4 - Van der Waals equation of state, first order phase transitions, critical point, law of corresponding state
  • Chapter 9 Part 5 - Critical Phenomena - A first encounter (Phenomena near critical point, order parameter, power laws, critical exponents)
  • Chapter 10 Part 1 - Critical Phenomena and Ferromagnetism (Phenomena of Ferromagnetism and Ising Model)
  • Chapter 10 Part 2 - Critical Phenomena and Ferromagnetism (Mean field Theory of Ising Model - Physical Idea)
  • Chapter 10 Part 3 - Critical Phenomena and Ferromagnetism (Mean Field Theory - critical exponents and formal approach)
  • Chapter 10 Part 4 - Critical Phenomena (Free energy as a function of m and Landau Theory of Continuous Phase Transition)
  • Chapter 10 Appendix A - The Percolation Problem
  • Chapter 10 Appendix B (Optional) - Metropolis Monte Carlo Algorithm of Ising Model
  • Chapter 10 Appendix C - Landau (Phenomenological) Theory of Continuous Transitions
  • Chapter 10 Appendix D (Optional) - The origin of J in the Ising model (the exchange interaction)
  • Chapter 11 - Grand Canonical Ensemble Theory (Systems with T,V,mu, Grand Partition Function, physics meaning, grand potential and connection to thermodynamics)
  • Intermission - Lead Sheets into Chapter 12 (Re-deriving Fermi-Dirac and Bose-Einstein distributions)
  • Chapter 12 - General Formulation of Ideal Fermi Gas and Ideal Bose Gas based on the grand partition function
  • Chapter 13 Part 1 - Ideal Fermi Gas (3D non-relativistic, relevant systems, general equations and relations)
  • Chapter 13 Part 2 - Ideal Fermi Gas (T=0 physics, Fermi energy, Fermi temperature, degenerate pressure)
  • Chapter 13 Part 3 - Ideal Fermi Gas (low-temperature physics, mu(T), E(T), heat capacity)
  • Chapter 13 Part 4 - Ideal Fermi Gas (General Equations rewritten and Correction to Classical ideal gas behavior)
  • Chapter 14 Part 1 (Optional) - Ideal Bose Gas (Essentials and Bose-Einstein Condensation)
  • Chapter 14 Part 1A (Optional) - Ideal Bose Gas (full version for low temperature physics)
  • Chapter 14 Part 2 (Optional) - Ideal Bose Gas (Experimental realization of Bose-Einstein Condensation)
  • Chapter 14 Part 3 (Optional) - Ideal Bose Gas (Correction to classical ideal gas law at high temperature)
  • Chapter 15 - Summary and References
  • Further Reading -- At PHYS4031 level and beyond


  • Problem Sets
  • Declaration of Honesty in Academic Work - Blank Form
  • Problem Set 1 (due 19 September 2016)
  • Problem Set 2 (due 30 September 2016)
  • Problem Set 3 (due 12 October 2016)
  • Problem Set 4 (due 21 October 2016)
  • Problem Set 5 (due 8 November 2016)
  • Problem Set 6 (due 22 Nov 2016)


  • Sample Questions for Exercise Classes
  • Exercise-Class-Week1-2016
  • Exercise-Class-Week2-2016
  • Exercise-Class-Week3-2016
  • Exercise-Class-Week4-2016
  • Exercise-Class-Week5-2016
  • Exercise-Class-Week6and7 2016
  • Exercise-Class-Week7and8 2016
  • Exercise-Class-Week8and9-2016-revised
  • Exercise-Class-Week10-2016
  • Exercise-Class-Week11-2016
  • Exercise-Class-Week12-2016
  • Exercise-Class-Week13-2016
  • Sample Question-Extra-2016