Important Notes for Users of Mac OS X 10.12 (Sierra) or Later
Because of the security enhancement made in 10.12, many (freely-available) applications downloaded from anywhere out of the App Store may fail, which is known as an "App Translocation" problem. To avoid this and run SPECTRA correctly, the users should once move the executable file ("spectra" application file in the SPECTRA directory, or more correctly "spectra.app" directory) to somewhere out of the SPECTRA directory, then return it to the original location.
In 10.15 (Catalina, and maybe in 10.16 or later), you need to run "spectra" by right-click (or holding the Control key) and "open" (maybe you need to do this twice). In addition, the solvers ("spectra_solver_nompi", and "spectra_solver" for parallel computing) and the parameter file converter ("conv_spectra") should be run by the same procedure. This process is needed only once (for the first time you run SPECTRA).
If the above procedure does not work, please try to remove the extended attributes of the whole directory (xattr -rc spectra).