Heitler-London paper

In the third part of the paper Huckel derives energy expressions for the different electronic terms of benzene using method 1. The wavefunction is given as a Slater determinant, and the solution of the Schrodinger equation is expressed in analogy to the Heitler-London paper [1] as... 

Though the success of the Heitler-London paper heralded, at the same time, the deadlock of their approach, the very next phase in the development of quantmn chemistry was full of new promises two theoretical schemata established themselves... 

Dirac s 1929 pronouncement encapsulated what was already part of the physicists culture for many decades. And, with Dirac s specific contributions to the development of quantum mechanics, it became possible to artictrlate this reductionist program Chemistry after the Heitler-London paper could be perceived as being the different manifestations of spin, and spin, after all, was under the jurisdiction of the physicists. And though physicists believed that the new quantum mechanics had also taken care of chemistry, the chemists themselves did not appear to have been under any panic that their identity was being transformed and they were being turned into physicists. 

The Heitler-London papers mark the birth of VB theory [2], which was developed by Pauling as a quantum mechanical version of the Lewis model. This quantum mechanical articulation of Lewis shared-pair model has culminated in a generalizing intellectual constmct [25], which described the electron-pair bond A-X as a superposition of covalent (cov) and ionic forms, a+x— and 4>a—x+ [Eq. (2a) and (2b)]. 

Instead of formulating the wave function for a crystal as a sum of functions describing various ways of distributing the electron-pair bonds among the interatomic positions, as was done in the first section of this paper, let us formulate it in terms of two-electron functions describing a single resonating valence bond. A bond between two adjacent atoms ai and cq- may be described by a function < i3-(l, 2) in which 1 and 2 represent two electrons and the function i may have the simple Heitler-London form... 

Quantum mechanics was the dominant theory in chemistry even before the advent of electronic computers. The conventional date for the beginning of this period may be fixed at 1927 with the publications of the Heitler and London paper on hydrogen molecule [3]. The growth of theoretical chemistry (or better, theoretical quantum chemistry) between 1930 and 1960 (thirty years, again, as for the last period) has followed a research programme different from that accepted in the most recent period. 

Just before returning to Europe in 1929, Slater generalized into an N-electron system the wave function used by Pauling in the treatment of helium in the 1928 Chemical Reviews essay. The title of Slater s paper, "The Self-Consistent Field and the Structure of Atoms," shows his debt to Hartree, although Slater s method turned out to be a great deal more practical than Hartree s, as well as consistent with the methods of Heitler, London, and Pauling.70... 

Equations (1.105) and (1.106) are the Heitler-London counterpart of the corresponding quantities (Equations 3.4 and 3.5 on page 340 of Ruedenberg s paper (1962), which refers to a LCAO-MO wave function. Ruedenberg calls Equation (1.106) the modification of the quasi-classical density due to the interference effect , while we, more literally, speak of exchange[a(r)b(r)], [b(r)a(r)] and overlap[—Sa1(r)], [—Sfe2(r)] densities. Finally, it is worth noting that, while ... 

Calculations of the lowest excitonic states in anthracene were performed by Silbey et al. (74), Craig (12), Fox and Yatsiv (75), Davydov and Sheka (76), and Claxton (77) within the Heitler-London approximation. In the papers by Silbey et al. (74), Craig (12), Fox and Yatsiv (75), and Claxton (77), only the states k 0 were considered, and the mixing of molecular configurations has been taken into account. Davydov and Sheka (76) have neglected the mixing of molecular configurations, but for some directions of the wavevector they obtained the form of excitonic bands by means of the Heitler-London approximation. 

G. Corongiu, The HEHHE method a combination of Hartree-Eock and Heitler-London approximations. Invited paper, Sanibel Symposium 2005. 

Only the first of these truly originates from him. In the first paper of the series, Pauling took up the idea of spatially directed bonds. By a generalization of the Heitler-London model for hydrogen, a normal chemical bond can be associated with the spin pairing of two electrons, one from each of the two atoms. While an s orbital is spherically symmetrical, other atomic... 

This paper attracted Pauling s attention, who recognized that the Heitler-London procedure could not only be extended to larger molecules but also serve as a bridge between Lewis classical idea of chemical bond and the new quantum theory. In a series of papers ", where he introduced the concepts of hybridization, resonance, electronegativity, etc., and also in a famous book that influenced many generations of chemists, Pauling developed his ideas which formed the basis of the classical Valence-Bond theory. 

Let us look into a little more detailed aspects of the cmrent and future perspective for chemical d3mamics. As noted above, the foimdations of theoretical chemistry were already established in the 1920 s (both the papers of Born-Oppenheimer and Heitler London were published in 1927) and 1930 s (Landau and Zener published in 1932, and the transition state theory of Eyring and Evans-Polan3d was almost simultaneously launched in 1935), and even today the basic framework remains essentially the same. However, there are many reasons we need to promote the electronic-state theory into the realm of d3mamical electron theory by taking explicit account of time t in it. Below are listed some of the current attempts to achieve this goal. 

U]nfortunate that this treatise wiU almost certainly tend to fix, even more than has been done by the author s excellent papers, the viewpoint of most chemists on this, and only this one, approach to the problem of the chemical bond. It appears likely that the Heitler-London-Slater-Paultng method will entirely eclipse, in the minds of chemists, the single electron molecular... 

By the time of the 1970 Maryland Conference, which discussed how computational support for theoretical chemistry could be efficiently achieved, it was clear to all quantum chemists that many changes had occurred since the publication of the Heitler and London paper in 1927. Fostered by the organization of scientific meetings, the foundation of the new International Journal of Quantum Chemistry, the creation of summer and winter schools and of the Sanibel Island meetings, and the presence of computers and the developments in hardware and software, the practice of quantum... 

Wilson, E. B. 1977. Impact of the Heitler-London hydrogen molecule paper on chemistry. International Journal of Quantum Chemistry 11 17-28. 

---