Your History

Menu

Boltzmann Distribution of Microstates

Prerequisites

Boltzmann Normalization Constant/Partition Function | \(Z = Z(T) = \int_{\mathbf{s} \in S} \exp\left\{ - \frac{ E(\mathbf{s}) }{ T } \right\} d\mathbf{s}\)

Description

The Boltzmann distribution for a given system is used to define the probability of that system being in a certain microstate \( \htmlClass{sdt-0000000091}{\mathbf{s}} \) of all possible microstates \( \htmlClass{sdt-0000000026}{S} \). In physics, this is mostly applied to multi-particle systems, however the concept is generalizable to any stochastic system for which energy \( \htmlClass{sdt-0000000100}{E} \) and temperature \( \htmlClass{sdt-0000000029}{T} \) are defined.

\[p(\htmlClass{sdt-0000000091}{\mathbf{s}}) = \frac{1}{\htmlClass{sdt-0000000077}{Z}} \exp\left\{ - \frac{ \htmlClass{sdt-0000000100}{E}(\htmlClass{sdt-0000000091}{\mathbf{s}}) }{ \htmlClass{sdt-0000000029}{T} } \right\}\]

Symbols Used:

This symbol represents the temperature in a system.

\( Z \)

This symbol represents a normalizing factor for a function.

\( \mathbf{s} \)

This symbol represents a full description of the system taken at molecular level.

\( E \)

This symbol represents the energy.

Derivation

The energy-temperature ratio exponential is present by definition.

See the page Boltzmann Normalization Constant/Partition Function:

\[\htmlClass{sdt-0000000077}{Z} = \htmlClass{sdt-0000000077}{Z}(\htmlClass{sdt-0000000029}{T}) = \int_{\htmlClass{sdt-0000000091}{\mathbf{s}} \in \htmlClass{sdt-0000000026}{S}} \exp\left\{ - \frac{ \htmlClass{sdt-0000000100}{E}(\htmlClass{sdt-0000000091}{\mathbf{s}}) }{ \htmlClass{sdt-0000000029}{T} } \right\} d\htmlClass{sdt-0000000091}{\mathbf{s}}\]

for an explanation of the necessity for using the factor \( \frac{1}{ \htmlClass{sdt-0000000077}{Z} } \), as well as this factor's value in the continuous and discrete probability cases.

References

  1. Jaeger, H. (n.d.). Neural Networks (AI) (WBAI028-05) Lecture Notes BSc program in Artificial Intelligence. Retrieved June 9, 2024, from https://www.ai.rug.nl/minds/uploads/LN_NN_RUG.pdf