At the time Heitler received his doctorate, three Institutes for Theoretical Physics formed a consortium which worked on the key problems of the day, such as atomic and molecular structure, and exchanged both scientific information and personnel in their scientific quests. These institutes were located at the LMU, under Arnold Sommerfeld, the University of Göttingen, under Max Born, and the University of Copenhagen, under Niels Bohr. Furthermore, Werner Heisenberg and Born had just recently published their trilogy of papers which launched the matrix mechanics formulation of quantum mechanics.W. Heisenberg, Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen, Zeitschrift für Physik 33 879–893, 1925 (received 29 July 1925). [English translation in: B. L. van der Waerden, editor, Sources of Quantum Mechanics (Dover Publications, 1968) (English title: Quantum-Theoretical Re-interpretation of Kinematic and Mechanical Relations).]M. Born and P. Jordan, Zur Quantenmechanik, Zeitschrift für Physik 34 858–888, 1925 (received 27 September 1925). [English translation in: B. L. van der Waerden, editor, Sources of Quantum Mechanics (Dover Publications, 1968) ]M. Born, W. Heisenberg, and P. Jordan, Zur Quantenmechanik II, Zeitschrift für Physik 35 557–615, 1925 (received November 1925). [English translation in: B. L. van der Waerden, editor, Sources of Quantum Mechanics (Dover Publications, 1968) ] Also, in early 1926, Erwin Schrödinger, at the University of Zurich, began to publish his quintet of papers which launched the wave mechanics formulation of quantum mechanicsErwin Schrödinger (From the German) Quantization as an Eigenvalue Problem (First Communication), Annalen der Physik 79 (4) 361–376, 1926. [English translation in Gunter Ludwig Wave Mechanics 94–105 (Pergamon Press, 1968) ]Erwin Schrödinger (From the German) Quantization as an Eigenvalue Problem (Second Communication), Annalen der Physik 79 (6) 489–527, 1926. [English translation in Gunter Ludwig Wave Mechanics 106–126 (Pergamon Press, 1968) ]Erwin Schrödinger (From the German) Quantization as an Eigenvalue Problem (Third Communication), Annalen der Physik 80 (13) 437–490, 1926.Erwin Schrödinger (From the German) Quantization as an Eigenvalue Problem (Fourth Communication), Annalen der Physik 81 (18) 109–139, 1926. [English translation in Gunter Ludwig Wave Mechanics 151–167 (Pergamon Press, 1968) ] and showed that the wave mechanics and matrix mechanics formulations were equivalent.Erwin Schrödinger (From the German) On the Relationship of the Heisenberg-Born-Jordan Quantum Mechanics to Mine, Annalen der Physik 79 (8) 734–756, 1926. [English translation in Gunter Ludwig Wave Mechanics 127–150 (Pergamon Press, 1968) ] These papers immediately put the personnel at the leading theoretical physics institutes onto applying these new tools to understanding atomic and molecular structure. It was in this environment that Heitler went on his Rockefeller Foundations Fellowship, leaving LMU and within a period of two years going to do research and study with the leading figures of the day in theoretical physics, Bohr's personnel in Copenhagen, Schrödinger in Zurich, and Born in Göttingen.
