Jan Korringa (31 March 1915 – 9 October 2015) was a Dutch American Theoretical Physicist, specializing in theoretical condensed matter physics. He also contributes to the KKR Method. Education and career Korringa received an undergraduate degree from Delft University of Technology. In 1937, Korringa went to Leiden University to pursue graduate studies. Due to the closure of Leiden University, Korringa returned to Delft University of Technology. In 1942, he received a Doctor of Philosophy from Delft University of Technology and published his thesis, Onderzoekingen op het gebied algebraïsche optiek (Essays in the area of algebraic optics). In 1946, Korringa became an associate professor at the University of Leiden. He was a protégé of Hendrik Kramers, who had been the first protégé of Niels Bohr; a large influence on his interest in quantum mechanics. In 1952, Korringa went to the United States and accepted a full professorship at Ohio State University. He was a consultant at Oak Ridge National Laboratory for many years. During the summers, he collaborated with a group at Chevron Corporation that developed nuclear magnetic resonance logging. In 1962, he was awarded a Guggenheim Foundation fellowship that he used for a sabbatical at the University of Besançon in France. In a 1947 paper, Korringa showed how his multiple scattering theory (MST) could be used to find the energy as a function of wavevector for electrons in a periodic solid. In 1954, Nobel laureate Walter Kohn and Norman Rostoker, who went on to have a successful career in nuclear physics, derived the same equations using the Kohn variational method. Two of Korringa's students, Sam Faulkner and Harold Davis, started a program at the Oak Ridge National Laboratory using the Korringa-Kohn-Rostoker (KKR) band-theory equations to calculate the properties of solids. The KKR equations are now used around the world and are the subject of several books. Korringa realized that his equations could be used to calculate the electronic states of nonperiodic solids for which Bloch’s theorem does not hold. In 1958 he published an approach, now called the average t-matrix approximation, for calculating the electronic states in random substitutional alloys. That work continued to evolve and was later connected to the higher-level theory called the Coherent Potential Approximation (CPA). Balázs Győrffy and Malcolm Stocks combined it with the KKR theory to obtain the KKR–CPA method, which is presently used for alloy calculations. Korringa’s MST is the basis for numerous theoretical