He is a Research Professor at the Consejo Superior de Investigaciones Científicas (CSIC). After obtaining his Doctorate in Physics at the Universidad Autónoma de Madrid (1992), he spent three years at the University of Illinois (USA) as a Postdoctoral Associate, and was Associate Professor at the University of Oviedo from 1995 to 1999. He joined the Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC) in 1999, and later the Centro de Investigación en Nanociencia y Nanotecnología (CIN2), in 2007. Since 2012 he has been director of the Catalan Institute of Nanoscience and Nanotechnology Foundation (ICN2).
His research focuses on computer simulation of materials at the atomic scale, using quantum mechanics methods. He has developed computationally highly efficient schemes, which allow simulations of the behavior of complex materials able to reach size and time scales much larger than those allowed by traditional numerical methods. In particular, he is one of the principal creators of the SIESTA code that allows calculations of electronic structure and simulations of atomic dynamics in very complex molecules and solids, and which is used by thousands of researchers worldwide. He is currently one of the leading researchers of the MaX Center of Excellence (Materials Design at the Exascale), a European initiative on the frontier of high performance and high throughput computing technologies, which is adapting these codes to the most powerful current and future supercomputers.
Its current interests include electronic and thermal transport in nanometric devices, and 2D materials such as graphene, among many others. He has published more than 190 scientific articles and received over 23,000 citations. He is co-founder of the SIMUNE spin-off company, which provides computer simulation services to companies that develop technological innovation based on new materials.
Under his direction, the ICN2 obtained in 2014 the accreditation as Severo Ochoa Center of Excellence by the Spanish Ministry of Economy and Competitiveness, and participated in 2015 as one of the founding institutions of the Barcelona Institute of Science and Technology Private Foundation (BIST), of which Prof. Ordejon is member of the Board of Trustees. He is a Fellow of the American Physical Society and a member of the Academia Europaea.