Abstract
This chapter presents a pedagogical introduction to the variational methods in statistical thermodynamics. We start with some general considerations of the variational nature of thermodynamics, which is rooted in the second law, and manifested in the maximum-term method in the evaluation of the partition function in statistical mechanics. We present two common mathematical variational techniques, one based on the Gibbs-Bogoliubov-Feynman (GBF) variational bound and one based on the saddle-point (or steepest-descent) method. We illustrate the use of these techniques in the derivation of the mean-field theory for Ising model and the Poisson-Boltzmann equation. We also show that the GBF method provides a self-consistent treatment of fluctuation effects in weakly correlated systems.
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References
The uncertainty principle also takes the form of an inequality, but it can be deduced from the fundamental equations of quantum mechanics, e.g., the Schrödinger equation
H.B. Callen, Thermodynamics and an Introduction to Thermostatistics, 2nd edn. (Wiley, New York, 1985)
A.H. Nayfeh, Introduction to Perturbation Techniques (Wiley, New York, 1981)
T.L. Hill, Introduction to Statistical Thermodynamics (Dover, New York, 1986)
A. Ishihara, J. Phys. A Gen. Phys. 1, 539 (1968)
R.P. Feynman, Statistical Mechanics: A Set of Lectures (Addison- Wesley, Redwood, 1972)
H. Kleinert, Path Integrals in Quantum Mechanics, Statistics, and Polymer Physics, 2nd edn. (World Scientific, Singapore, 1995)
D. Amit, Field Theory, Critical Phenomena and Renormalization Group, 2nd edn. (World Scientific, Singapore, 1984)
P.-G. de Gennes, Scaling Concepts in Polymer Physics (Cornell University Press, Ithaca, 1979)
G.H. Fredrickson, The Equilibrium Theory of Inhomogeneous Polymers (Oxford University Press, New York, 2005)
A.L. Fetter, J.D. Walecka, Quantum Theory for Many-Particle Systems (Dover, Mineola, 2003)
J.-P. Hansen, I.R. McDonald, Theory of Simple Liquids, 2nd edn. (Academic Press, London, 1990)
P.M. Chaikin, T.C. Lubensky, Principles of Condensed Matter Physics (Cambridge University Press, Cambridge, 2000)
R.D. Coalson, A. Duncan, J. Chem. Phys. 97, 5653 (1992)
R.R. Netz, H. Orland, Euro. Phys. J. E 1, 203 (2000)
Because of the complex nature of the action in Eq. 8.23, the GBF bound does not hold, i.e., the true free energy is not always approached from above. D. Frydel has derived an set of exact relations based on the dual representation of the system—the original physical representation and the field-transformed representation. In the case of a two-parameter Gaussian reference, it is shown that the first two relations yield results identical to those by taking the stationary point of the variational action. See: D. Frydel, Eur. J. Phys.36, 065050 (2015)
R.R. Netz, H. Orland, Eur. Phys. J. E 11, 310 (2003)
M.M. Hatlo, R.A. Curtis, L. Lue, J. Chem. Phys. 128, 164717 (2008)
Z.-G. Wang, Phys. Rev. E 81, 021501 (2010)
This can be understood by noting that the electrostatic energy of a charged body is \(\frac{1}{2} \int d {\bf r} \rho ({\bf r}) \psi ({\bf r})\) and the electrostatic potential is in turn \(\psi ({\bf r})=\int d {\bf r}^{\prime } G ({\bf r}, {\bf r}^{\prime }) \rho ({\bf r}^{\prime })\). For a point charge at \({\bf r}_1\), we then obtain the energy as \(\frac{1}{2}G({\bf r}_1,{\bf r}_1)\)
R. Wang, Z.-G. Wang, J. Chem. Phys. 142, 104705 (2015)
R. Wang, Z.-G. Wang, J. Chem. Phys. 139, 124702 (2013)
M. Doi, S.F. Edwards, The Theory of Polymer Dynamics (Oxford University Press, New York, 1986)
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Wang, ZG. (2017). Variational Methods in Statistical Thermodynamics—A Pedagogical Introduction. In: Wu, J. (eds) Variational Methods in Molecular Modeling. Molecular Modeling and Simulation. Springer, Singapore. https://doi.org/10.1007/978-981-10-2502-0_1
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DOI: https://doi.org/10.1007/978-981-10-2502-0_1
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