After the War, Herzfeld returned to the University of Vienna, however, the University was in such dire financial straits that he moved to Munich in 1919, with the intent of studying analytical chemistry and getting a job in the German chemical industry, which had a highly respected reputation. First, he was an assistant at the physico-chemical laboratory of Kasimir Fajans at Ludwig Maximilians University of Munich (LMU). However, once there, he found the challenge of theoretical physics more to his liking. He became Privatdozent for theoretical physics and physical chemistry at LMU, and therefore was much more associated with Arnold Sommerfeld, who was ordinarius professor for theoretical physics and Director of the Institute for Theoretical Physics – a prominent organization for the study of atomic and molecular structure. From 1925, until he left LMU in 1926, he was extraordinarius professor of theoretical physics. During this time, Linus Pauling did postdoctoral studies with him, and he was the thesis advisor for Walter Heitler, who got his doctorate in 1926. In 1925, Herzfeld published his book on kinetic theory and statistical mechanics, which became a graduate-level textbook in German-speaking universities.