Boltzmann Distribution of Microstates

Prerequisites

Description

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

Equation

\[p(\htmlId{tooltip-microstate}{\mathbf{s}}) = \frac{1}{\htmlId{tooltip-partitionFunction}{Z}} \exp\left\{ - \frac{ \htmlId{tooltip-systemEnergy}{E}(\htmlId{tooltip-microstate}{\mathbf{s}}) }{ \htmlId{tooltip-temperature}{T} } \right\}\]

Symbols Used

\(T\)

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:

\[\htmlId{tooltip-partitionFunction}{Z} = \htmlId{tooltip-partitionFunction}{Z}(\htmlId{tooltip-temperature}{T}) = \int_{\htmlId{tooltip-microstate}{\mathbf{s}} \in \htmlId{tooltip-microstateSpace}{S}} \exp\left\{ - \frac{ \htmlId{tooltip-systemEnergy}{E}(\htmlId{tooltip-microstate}{\mathbf{s}}) }{ \htmlId{tooltip-temperature}{T} } \right\} d\htmlId{tooltip-microstate}{\mathbf{s}}\]

for an explanation of the necessity for using the factor \( \frac{1}{ \htmlId{tooltip-partitionFunction}{Z} } \), 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

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