He belongs to the remarkable school of Scandinavian physicians and theoretical chemists, the Professor Roos in the late sixties took over scientists like the Professor Ingrid Fischer-Hjalmars and the Professor Per-Olof Löwding in an emerging science as computational quantum chemistry.

Particularly, the Professor Roos is the father of muliticonfiguration quantum chemistry, which he represents at all levels. Some of his most important milestones are; Development of the algorithm called CI direct in 1972 and the MOLCAS platform of quantum chemical calculations (1988-2006).

He is a scientist of international renown whose achievements have guided and defined the development of a branch of chemistry still young such as theoretical chemistry, and also giving to other researchers the access to this one through the MOLCAS programme or by the schools of Quantum Chemistry.

His reputation is supported by his membership to the Nobel Committee of Chemistry of the Royal Swedish Academy between 1986 and 2000, and his standing committee for the awarding of the Nobel Prize since 1992.