Question: Friedrich Hund, creator of Hund's rule of maximum multiplicity, is known for his work on what?
Context: Gerhard Friedrich Hund (February 4, 1932 Leipzig) is a German chess player, mathematician and computer scientist. Colin de Verdière's invariant is a graph parameter formula_1 for any graph "G," introduced by Yves Colin de Verdière in 1990.  It was motivated by the study of the maximum multiplicity of the second eigenvalue of certain Schrödinger operators. In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy to distinguish it from Helmholtz free energy) is a thermodynamic potential that can be used to calculate the maximum of reversible work that may be performed by a thermodynamic system at a constant temperature and pressure (isothermal, isobaric).  The Gibbs free energy (J in SI units) is the "maximum" amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter); this maximum can be attained only in a completely reversible process.  When a system transforms reversibly from an initial state to a final state, the decrease in Gibbs free energy equals the work done by the system to its surroundings, minus the work of the pressure forces. Friedrich Hermann Hund (4 February 1896 – 31 March 1997) was a German physicist from Karlsruhe known for his work on atoms and molecules. William P. Bengen is a retired financial adviser who first articulated the 4% withdrawal rate ("Four percent rule") as a rule of thumb for withdrawal rates from retirement savings in ; it is often known as the "Bengen rule" in his honor.  The rule was later further popularized by the Trinity study (1998), based on the same data and similar analysis.  Bengen later called this rate the SAFEMAX rate, for "the maximum 'safe' historical withdrawal rate", and revised it in to 4.5% if tax-free and 4.1% for taxable. Hund's rule of maximum multiplicity is a rule based on observation of atomic spectra, which is used to predict the ground state of an atom or molecule with one or more open electronic shells.  The rule states that for a given electron configuration, the lowest energy term is the one with the greatest value of spin multiplicity.  This implies that if two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs.  The rule, discovered by Friedrich Hund in 1925, is of important use in atomic chemistry, spectroscopy, and quantum chemistry, and is often abbreviated to Hund's rule, ignoring Hund's other two rules. In mathematics, Newton's identities, also known as the Newton–Girard formulae, give relations between two types of symmetric polynomials, namely between power sums and elementary symmetric polynomials. Evaluated at the roots of a monic polynomial "P" in one variable, they allow expressing the sums of the "k"-th powers of all roots of "P" (counted with their multiplicity) in terms of the coefficients of "P", without actually finding those roots.  These identities were found by Isaac Newton around 1666, apparently in ignorance of earlier work (1629) by Albert Girard.  They have applications in many areas of mathematics, including Galois theory, invariant theory, group theory, combinatorics, as well as further applications outside mathematics, including general relativity. Cope's rule, named after American paleontologist Edward Drinker Cope, postulates that population lineages tend to increase in body size over evolutionary time.  It was never actually stated by Cope, although he favoured the occurrence of linear evolutionary trends.  It is sometimes also known as the Cope-Depéret rule, because Charles Depéret explicitly advocated the idea.  Theodor Eimer had also done so earlier.  The term "Cope's rule" was apparently coined by Bernhard Rensch, based on the fact that Depéret had "lionized Cope" in his book.  While the rule has been demonstrated in many instances, it does not hold true at all taxonomic levels, or in all clades. Larger body size is associated with increased fitness for a number of reasons, although there are also some disadvantages both on an individual and on a clade level: clades comprising larger individuals are more prone to extinction, which may act to limit the maximum size of organisms. 5-Dehydro-"m"-xylylene (DMX) is an aromatic organic triradical and the first known organic molecule to violate Hund's Rule. In atomic physics, Hund's rules refers to a set of rules that German physicist Friedrich Hund formulated around 1927, which are used to determine the term symbol that corresponds to the ground state of a multi-electron atom.  The first rule is especially important in chemistry, where it is often referred to as, simply, Hund's Rule.
Answer: known for his work on atoms and molecules.