README.md

ACE (Atmospheric Chemical Equilibrium)

Fortran code that computes the chemical equilibrium composition for a given

• elemental composition
• pressure-temperature profile

The code can be typically used to compute the chemical equilibrium composition in atmospheres of AGB stars, brown dwarfs, and exoplanets.

ACE is based on the algorithm implemented in the NASA/CEA program, which is described in Gordon & McBride 1994, NASA Reference Publication 1311, 1.

If you use ACE for your work, I would appreciate if you cite the papers

• Agúndez et al. 2020, A&A, 637, A59
• Agúndez 2025, A&A, 699, A306

Inquiries can be sent to marcelino.agundez@csic.es

Compilation:

Download and uncompress the zip file. This will create two directories:

• src
• examples

You need to have gfortran installed in your system. Compilation has been tested with gfortran. Other fortran compilers such as ifort may work but they have not been tested. To compile simply type:

$ cd src

$ make clean (only needed if the code has been compiled previously)

$ make

This should have created a binary file named ace. It is convenient to move the binary file to the local directory of your system bin where binaries are located. This allows you to run the code simply typing ace in any folder without the need to duplicate binaries.

Usage:

In the directory examples you have two sub-directories named agb and exoplanet. These sub-directories contain specific input files to run ACE for AGB and exoplanet atmospheres. The file ace.inpcontains the input file names of the models to be run, e.g., model_xx.inp. Each input file model_xx.inp contains in turn three file names with extensions:

• .apt (altitude-pressure-temperature profile, the altitude is a dummy variable)
• .spec (species file)
• .therm (thermochemical data file)

To run ACE, move to corresponding sub-directory and simply type:

$ ace (assuming you have the binary in the bin folder of your system)

In the directory agb there are thermochemical data for gaseous and condensed species. ACE can in principle deal with mixtures of gaseous and condensed species. However, in the practice the code usually crashes when multiple condensed species are included.