.castep_bin files contain the numerical output of a CASTEP job
in binary format. The difference between the two files is that the
.check file stores electronic wavefunctions in
addition to all other information (calculation parameters, structure, electron density, electronic, and vibrational properties) and
can become very large for large systems.
At least one of these files is required by the Materials Studio client to analyze CASTEP results. The CASTEP module in Materials Studio allows you to choose which of the two binary files to download after job execution.
Visualization of orbitals or of STM images requires information about
electronic wavefunctions, hence the
.check file is always downloaded if any of these properties were requested.
CASTEP file formats