Fermi-Dirac Functions


Astronomy Research
   Radiative Opacity
   2024 Neutrino Emission from Stars
   2023 White Dwarfs & 12C(α,γ)16O
   2023 MESA VI
   2022 Earendel, A Highly Magnified Star
   2022 Black Hole Mass Spectrum
   2021 Skye Equation of State
   2021 White Dwarf Pulsations & 22Ne
   Software Instruments
     Stellar equation of states
     EOS with ionization
     EOS for supernovae
     Chemical potentials
     Stellar atmospheres

     Voigt Function
     Jeans escape
     Polytropic stars
     Cold white dwarfs
     Adiabatic white dwarfs

     Cold neutron stars
     Stellar opacities
     Neutrino energy loss rates
     Ephemeris routines
     Fermi-Dirac functions

     Polyhedra volume
     Plane - cube intersection
     Coating an ellipsoid

     Nuclear reaction networks
     Nuclear statistical equilibrium
     Laminar deflagrations
     CJ detonations
     ZND detonations

     Fitting to conic sections
     Unusual linear algebra
     Derivatives on uneven grids
     Pentadiagonal solver
     Quadratics, Cubics, Quartics

     Supernova light curves
     Exact Riemann solutions
     1D PPM hydrodynamics
     Hydrodynamic test cases
     Galactic chemical evolution

     Universal two-body problem
     Circular and elliptical 3 body
     The pendulum


     Zingale's software
     Brown's dStar
     GR1D code
     Iliadis' STARLIB database
     Herwig's NuGRID
     Meyer's NetNuc

AAS Journals
   2024 AAS YouTube
   2024 AAS Peer Review Workshops

2024 ASU Energy in Everyday Life
2024 MESA Classroom
Outreach and Education Materials

Other Stuff:
   Bicycle Adventures

Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.

The terms "Fermi-Dirac", "generalized Fermi-Dirac", and "Fermi" function haven't received uniform usage in the literature. I'll use "Fermi-Dirac" for the two parameter integral: \begin{equation} F_{k}(\eta,\theta) = \int\limits_{0}^{\infty} \ {x^{k} \ (1 + 0.5 \ \theta \ x)^{1/2} \over \exp(x - \eta) + 1} \ dx \label{eq1} \tag{1} \end{equation} where $k$ is the order of the function, $\theta = k_B T / (mc^2)$ is the relativity parameter, and $\eta = \mu/(k_B T)$ is the normalized chemical potential energy $\mu$, which is sometimes called the degeneracy parameter. I'll use "Fermi" function as the $\theta=0$ special case of the Fermi-Dirac function: \begin{equation} F_{k}(\eta) = \int\limits_{0}^{\infty} \ {x^{k} \ \over \exp(x - \eta) + 1} \ dx \label{eq2} \tag{2} \end{equation} The Fermi functions can be obtained from some remarkable rational function approximations. The Fermi-Dirac function are solved by two methods. The first uses simpson integration on nested grids in tandem with integral transformations. The second method uses quadrature summations (Also see this article). The answers these methods produce are compared in fermi_dirac.tbz. My contributions to fermi_dirac.tbz include adding the first and second partial derivatives to the quadrature method, and gathering the various quadrature accuracies under one roof.

To see how these Fermi-Dirac functions are used in a bare knuckle stellar equation of state, peek at the Timmes eos instrument.


First derivatives with respect to η and θ
* *

Second derivatives with respect to η and θ
* * *

Please cite the relevant references if you publish a piece of work that use these codes, pieces of these codes, or modified versions of them. Offer co-authorship as appropriate.