During his graduate studies, he was influenced by Professors Sherrill D. Christian, Jack Cohn and Cedomir Sliepcevich, and by correspondences with Berni Alder, Bill Hoover, E. Brian Smith and Ben Widom.
Carnahan's vision of molecular interactions and fluid behavior was strongly influenced by the works of Johannes Diderik van der Waals and by René Descartes.
His interest in statistical mechanics, physics of fluids, molecular phenomena and fundamentals of equations of state led to the development of the Carnahan-Starling equation of state (1969)[2] for the fluid phase of rigid non-attracting spheres, as single components and mixtures (Mansoori-Carnahan-Starling-Leland, 1971)[3] After completion of his doctoral studies at University of Oklahoma, in 1971, he began a long research and teaching association with Professors Riki Kobayashi[citation needed] and Thomas W. Leland, Jr.,[citation needed] at Rice University in Houston, Texas.
In the 1980s, he resumed work on extending the Carnahan-Starling equation of state to systems of rigid non-attracting non-spherical particles.
Together with Professor Erich A. Muller,[citation needed] a series of papers were published in which a shape factor concept was incorporated to enable the equation developed for rigid sphere fluids to be extended to describe the fluid phase of many rigid nonattracting nonspherical particles.