FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres

For the calculation of complex neutral/ionized gas-phase chemical equilibria, we present a semi-analytical, versatile, and efficient computer program, called FastChem. The applied method is based on the solution of a system of coupled non-linear (and linear) algebraic equations, namely the law of mass action and the element conservation equations including charge balance, in many variables. Specifically, the system of equations is decomposed into a set of coupled nonlinear equations in one variable each, which are solved analytically whenever feasible to reduce computation time. Notably, the electron density is determined by using the method of Nelder and Mead at low temperatures. The program is written in object-oriented C++ which makes it easy to couple the code with other programs, although a stand-alone version is provided. FastChem can be used in parallel or sequentially and is available under the GNU General Public License version 3 at https://github.com/exoclime/FastChem together with several sample applications. The code has been successfully validated against previous studies and its convergence behaviour has been tested even for extreme physical parameter ranges down to 100K100K and up to 1000bar1000bar⁠. FastChem converges stable and robust in even most demanding chemical situations, which posed sometimes extreme challenges for previous algorithms.

• Publication year

  2018

• Venue

  Monthly notices of the Royal Astronomical Society

• Publication date

  2018-04-13

• Fields of study

  Chemistry, Physics, Computer Science, Environmental Science

• Identifiers
  DOI 10.1093/mnras/sty1531arXiv 1804.05010
• External record

  Open on Semantic Scholar

• Source metadata

  Semantic Scholar

• No claims are published for this paper.

• No concepts are published for this paper.

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