Statistical mechanics (rmgpy.statmech
)¶
The rmgpy.statmech
subpackage contains classes that represent various
statistical mechanical models of molecular degrees of freedom. These models
enable the computation of macroscopic parameters (e.g. thermodynamics, kinetics,
etc.) from microscopic parameters.
A molecular system consisting of \(N\) atoms is described by \(3N\) molecular degrees of freedom. Three of these modes involve translation of the system as a whole. Another three of these modes involve rotation of the system as a whole, unless the system is linear (e.g. diatomics), for which there are only two rotational modes. The remaining \(3N6\) (or \(3N5\) if linear) modes involve internal motion of the atoms within the system. Many of these modes are welldescribed as harmonic oscillations, while others are better modeled as torsional rotations around a bond within the system.
Molecular degrees of freedom are mathematically represented using the Schrodinger equation \(\hat{H} \Psi = E \Psi\). By solving the Schrodinger equation, we can determine the available energy states of the molecular system, which enables computation of macroscopic parameters. Depending on the temperature of interest, some modes (e.g. vibrations) require a quantum mechanical treatment, while others (e.g. translation, rotation) can be described using a classical solution.
Translational degrees of freedom¶
Class 
Description 

A model of threedimensional translation of an ideal gas 
Rotational degrees of freedom¶
Class 
Description 

A model of twodimensional rigid rotation of a linear molecule 

A model of threedimensional rigid rotation of a nonlinear molecule 

A model of onedimensional rigid rotation of a Krotor 

A model of threedimensional rigid rotation of a spherical top molecule 
Vibrational degrees of freedom¶
Class 
Description 

A model of a set of onedimensional harmonic oscillators 
Torsional degrees of freedom¶
Class 
Description 

A model of a onedimensional hindered rotation 
The Schrodinger equation¶
Class 
Description 

Calculate the partition function at a given temperature from energy levels and degeneracies 

Calculate the dimensionless heat capacity at a given temperature from energy levels and degeneracies 

Calculate the enthalpy at a given temperature from energy levels and degeneracies 

Calculate the entropy at a given temperature from energy levels and degeneracies 

Calculate the sum of states for a given energy domain from energy levels and degeneracies 

Calculate the density of states for a given energy domain from energy levels and degeneracies 
Convolution¶
Class 
Description 

Return the convolution of two arrays 

Convolve a degree of freedom into a density or sum of states using the BeyerSwinehart (BS) direct count algorithm 

Convolve a degree of freedom into a density or sum of states using the BeyerSwinehartSteinRabinovitch (BSSR) direct count algorithm 
Molecular conformers¶
Class 
Description 

A model of a molecular conformation 