His works have received over 22,000 citations. His research specialties are in
condensed matter theory, particularly in the field of excited state
electronic structure and the theory of
X-ray and electron spectra. One of Rehr's major accomplishment was the theoretical solution of the EXAFS problem, and quantitative theories of core-level x-ray and electron spectroscopies. Rehr is also the founding father of the first principles code
FEFF8 and the principal investigator of the FEFF project. Rehr group's FEFF codes are in use worldwide and currently has over thousands of subscription. Rehr has also led his team in developing next generation scientific computation on
cloud computing platforms; their FEFF programs are available in the
Amazon Web Services cloud for the physics community. FEFF leverages
Amazon Elastic Compute Cloud Computer instances to enable physicists all over the world to access on-demand
High Performance Computing resources. His research is supported by the US Department of Energy BES, the
DOE Computational Materials and Chemical Sciences Network (CMCSN) ==Honors and awards==