Cowan's atomic-structure codes, modernized for 64-bit systems

A. Kramida, Department of Astronomy, University of Maryland, College Park, MD, USA -- akramida @ umd.edu

Version 26.2.3dev -- work in progress toward the next release; the latest release is 26.2.2, November 10, 2026. See DOCS/CHANGES.md. Earlier versions were distributed from https://doi.org/10.18434/T4/1502500.

To see which version you have: on Windows, the Details tab of an executable's Properties in Explorer, or in PowerShell (Get-Item CODE\RCE20KD.exe).VersionInfo.FileVersion; on Linux and macOS, the VERSION= line of version.txt in the installed tree.

R. D. Cowan's programs for atomic energy levels, radiative transition wavelengths and probabilities, electron-impact excitation cross sections and photoionization cross sections, written by him between 1962 and 1991 and described in R. D. Cowan, The Theory of Atomic Structure and Spectra (University of California Press, Berkeley, 1981). The package holds the four main programs -- RCN, RCN2, RCG and RCE, as Fortran sources and as Windows executables -- the data files they read, and Python utility codes that prepare their input and interpret their output. Several people have contributed to them since; NOTICE.md says who. Write to the author with any question about their operation.

The package runs on Windows, Linux and macOS, with the same input decks, output files, utility codes and command names on all three. Executables are supplied for 64-bit Windows, with the gfortran runtime libraries they need; on Linux and macOS the four programs are compiled from FOR/ by one command.

The Windows build is the one the author uses daily. The Linux build has been verified end to end on x86-64 (Ubuntu 24.04, gfortran 13.3): the Pr III case gives a byte-identical TAPE2E on both systems. macOS has not been exercised -- it is expected to work, not tested; please report what you find.

• A 64-bit system with at least 16 GB of RAM. The executables are built for array dimensions that suit most tasks; for larger ones, recompile (DOCS/BUILDING.md).
• Python 3 for the utility codes, and numpy for true jj coupling (optional) and for calc_TP (required).
• gfortran on Linux and macOS; on Windows only to recompile.

No path in the package may contain a space. Details are in DOCS/INSTALL.md.

Windows -- in full in DOCS/INSTALL.md:

1. Install Python 3, with "Add python.exe to PATH"; pip install numpy.
2. Extract the zip archive, keeping its directories, e.g. to c:\COWAN.
3. Add c:\COWAN\CODE to the Path variable.
4. In c:\COWAN\WORK, run make_cfp. It builds the binary data decks RCG cannot run without.

Linux and macOS -- in full in DOCS/INSTALL.md:

chmod +x CODE/unix/*
CODE/unix/build.sh
CODE/unix/install.sh

and put on the PATH the line install.sh prints at the end.

From a directory holding the input files IN36 and IN2:

rcn
rcn2
rcg
rce

Each program reports NORMAL EXIT; run in WORK/, this is the installation test. After a least-squares fit with RCE, update11 carries the fitted parameters back into RCG's input and runs RCG again. On the first RCE run of a fit, rce --ground puts the calculated ground level at zero. Worked examples, each with its own README.txt, are in the subdirectories of WORK/.

Comparing with output of versions before 26.2.1: the physical constants were brought up to CODATA 2022 in 26.2.1, and some printed quantities moved slightly -- autoionization rates by +0.05 %. See DOCS/CHANGES.md.

The package is not covered by a single licence: see LICENSE.md and NOTICE.md.