John Clarke Slater (December 22, 1900 – July 25, 1976) was an American physicist who advanced the theory of the electronic structure of atoms, molecules and solids.

He then joined the Quantum Theory Project of the University of Florida as research professor, where the retirement age allowed him to work for another five years.

Slater was nominated for the Nobel Prize, in both physics and chemistry, multiple times,[8] and he received the National Medal of Science in 1970.

As he relates: Bohr was very nice, he invited me to Christmas dinner, I told him about my [photon] ideas, he felt these were fine, “But, you see, they’re much too definite."

These include statements affecting policies in physics education and research at large, and show his deep commitment to both.

At the personal level, Morse states: "Through most of (the 1930s) he looked more like an undergraduate than a department head ... he could render his guests weak with laughter simply by counting ... in Danish.

"[19] Returning in time to 1920, Slater had gone to Harvard to work for a Ph.D. with Percy Bridgman, who studied the behaviour of substances under very high pressures.

Slater measured the compressibility of common salt and ten other alkali halides—compounds of lithium, sodium, potassium and rubidium, with fluorine, chlorine and bromine.

This brought Slater's observation concerning the mechanical properties of ionic crystals into line with the theory that Bohr had based on the spectroscopy of gaseous elements.

He wrote the alkali halide paper in 1923, having "by the summer of 1922" been "thoroughly indoctrinated ... with quantum theory", in part by the courses of Edwin Kemble following a fascination with Bohr's work during his undergraduate days.

[20] Interest in this "old-quantum-theory" paper subsided with the arrival of full quantum mechanics, but Philp M. Morse's biography states that "in recent years it has been recognized that the correct ideas in the article are those of Slater.

A year by year selection, up to his switch to work relating to radar includes: In his memoir,[1] Morse wrote "In addition to other notable papers ... on ... Hartree's self-consistent field,[28] the quantum mechanical derivation of the Rydberg constant,[29] and the best values of atomic shielding constants,[31] he wrote a seminal paper on directing valency[32] " (what became known, later, as linear combination of atomic orbitals).

"[20] Slater's doctoral students, during this time, included Nathan Rosen Ph.D. in 1932 for a theoretical study of the hydrogen molecule, and William Shockley Ph.D. 1936 for an energy band structure of sodium chloride, who later received a Nobel Prize for the discovery of the transistor.

Slater, in his experimental and theoretical work on the magnetron (key elements paralleled his prior work with self-consistent fields for atoms[1]) and on other topics at the Radiation Laboratory and at the Bell Laboratories did "more than any other person to provide the understanding requisite to progress in the microwave field", in the words of Mervin Kelley, then head of Bell Labs, quoted by Morse.

[48] In the words of Robert Nesbet: "Slater founded the SSMTG with the idea of bringing together a younger generation of students and PostDocs with a common interest in the electronic structure and properties of atoms, molecules and solids.

He wrote "During the fifteen-year life of the group some sixty persons were members and thirty-four took doctoral degrees with theses connected with its work.

They were quoted widely for scientific and biographical content, in journal articles and government reports and libraries are starting to put them online.

Solid state work progressed more rapidly at first in the SSMTG, with contributions over the first few years by George F. Koster, John Wood, Arthur Freeman and Leonard Mattheis.

Robert Nesbet, Brian Sutcliffe, Malcolm Harrison and Levente Szasz brought in a variety of further approaches to molecular and atomic problems.

Jens Dahl, Alfred Switendick, Jules Moskowitz, Donald Merrifield and Russell Pitzer did further work on molecules, and Fred Quelle on solids.

Major pieces of work which he did coauthor dealt with applications of (1) group theory in band structure calculations[60] and (2) equivalent features of linear combination of atomic orbital (LCAO), tight binding and Bloch electron approximations, to interpolate results for the energy levels of solids, obtained by more accurate methods,[61] A partial list of members of the SSMTG (Ph.D. students, post-doctoral members, research staff and faculty, in some cases successively, labeled †, ‡, ৳, ¶), together with references that report their SSMTG and later activities, follows.

Distinguished visitors included Frank Boys, Alex Dalgarno, Ugo Fano, Anders Fröman, Inga Fischer-Hjalmars, Douglas Hartree, Werner Heisenberg, Per-Olov Löwdin, Chaim Pekeris, Ivar Waller and Peter Wohlfarth.

In the 1962 President's Report, Jay Stratton wrote (on p. 17) "A faculty committee under the chairmanship of Professor John C. Slater has taken primary responsibility for planning the facilities in the new Center for Materials.

He, Slater and Charles Townes, the provost, had been in close acquaintance since the early years of World War II, working on overlapping topics.

These included (1) members of the SSMTG and the CCL running quantum mechanical calculations and non-numeric applications[63] directed by Slater, Koster, Wood and Barnett, (2) the computer-aided design team of Ross, Coons and Mann, (3) members of the Laboratory for Nuclear Science, (4) Charney and Phillips in theoretical meteorology, and (5) Simpson and Madden in geophysics (from 1964 President's report, p. 336-337).

It took place at the end of Feynman's undergraduate days at MIT, when he wanted to stay on to do a Ph.D.[86] "When I went to Professor Slater and told him of my intentions he said: 'We will not have you here'.

He was exceptional in that he persisted in exploring atomic, molecular and solid state physics, while many of his peers were coerced by war, or tempted by novelty, to divert to nuclear mysteries.

[88] In August 2003, Alfred Switendick donated a collection of Quarterly Reports of the MIT Solid State and Molecular Theory Group (SSMTG), dating from 1951 to 1965.