Heitler-London, Pauling-Slater approach

Lewis concept . He reserved his major criticisms for the Heitler-London, Pauling-Slater (HLPS) approach ... 

Slater developed an approach (the "determinantal method") that offers a way of choosing among linear combinations (essentially sums and differences) of the polar and nonpolar terms in the Hund-Mulliken equations to bring their method into better harmony with the nonpolar emphasis characteristic of the Heitler-London-Pauling approach in which polar terms do not figure in the wave equation. 72... 

Slater s bond eigenfunctions constitute one choice (out of an infinite number) of a particular sort of basis function to use in the evaluation of the Hamiltonian and overlap matrix elements. They have come to be called the Heitler-London-Slater-Pauling (HLSP) functions. Physically, they treat each chemical bond as a singlet-coupled pair of electrons. This is the natural extension of the original Heitler-London approach. In addition to Slater, Pauling[12] and Eyring and Kimbal[13] have contributed to the method. Our following description does not follow exactly the discussions of the early workers, but the final results are the same. 

Historians would later credit Heitler, London, Slater, and Pauling with developing this approach to the chemical bond (in later years it would be called, in their honor, the HLSP theory). But most chemists would remember only Pauling, not only because he applied it to more molecules than the others, but because he alone among them was a chemist, able to communicate his results in a way that chemists understood. 

Although the aufbau approach of MO theory is adequate in all that follows, it may be useful for the sake of completeness to mention the rather more complicated method developed by Heitler, London, Slater, Pauling and others, and to stress that the two theories do not conflict. Both lead to approximations to the same charge density the difference is superficial and the same Fcynman-Hellman interpretation applies in each case. To appreciate this, it is sufficient to consider the molecule Hg. From the MO standpoint, the full two-electron wave function would be the product... 

Slater had been familiar with both approaches, from the early days of wave mechanics, partly as a result of his friendship with Mulliken. Although his name was associated with the Heitler-London-[Slater]-Pauling method after 1931, he was the first to point to the interrelationship of the two methods. In a short note. Slater came back to this topic and summarized his previous conclusions. He claimed once more that both methods were "complementary" rather than "antagonistic" and that the choice between the two should be made on the "basis of convenience rather than correctness" (Slater 1932, 255). The methods looked very different at first but when properly refined should come into closer agreement. Slater outlined the steps necessary for their refinement in the case of the valence bond method, one should allow for possible ways of... 

The application of Walter Heitler and Fritz London s valence bond theory was the first description of the binding forces in the H2 molecule, the simplest neutral molecule. Linus Pauling and John Slater later extended the principles to larger molecules.The key element in their proposal was the synthesis of a bonding wavefunction resulting from a combination of atomic orbitals that link the two atoms in a bond. It was hugely important that this localized approach concurred with the Lewis dot model. For the simplest neutral molecule, H2, the Hamiltonian operator may be written... 

This was first developed by Heitler and London in 1927 and later extended by Pauling and Slater in 1931. It is assumed that atoms complete with electrons, come together to form the molecule. The atoms retain their individuality and the bond is formed due to the interaction of valence electrons as the atoms approach each other. 

The publication of the papers by the Americans and especially those by Slater, Pauling, Van Vleck, and Mulliken prompted a rather desperate exchange of letters between Heitler and London starting in the end of 1935. This correspondence is quite revealing. It shows the attitude of each about the possible development of the approach laid down in their common paper, the tension between them, as well as the search for a means to consolidate their theory at a time when the Americans appeared to be taking over the field of quantum chemistry. The correspondence reflects the different style of their respective environments. Faithful to the Gottingen spirit, Heitler was... 

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