The pioneering work by Heitler and London and its subsequent development by Slater and Pauling are recalled. Modern formulation of the classical valence bond (VB) theory is briefly sketched. Its fundamental contribution to our understanding of chemical bonds, of electronic and geometric structure of molecules and of their properties is reminded. The generalized Heitler-London (GHL) theory provides a straightforward way to express the potential energy surface of H_3 in terms of Coulomb and exchange energies which can be calculated either by perturbation theory or using the surface integral method (SIM). By applying the Rayleigh-Schroedinger perturbation theory, GHL theory for the quartet spin state of H_3 is shown to yield results Heitler and London broke down the interaction energy between two H atoms (Fig. 4), noticing that a plot of the so-called quasi-classical contribution E 11, which is based on the Coulombic Schrödinger's equation in wave mechanics (1926) proved to be useful for solving problems in chemistry, beginning with the Heitler and London published work in 1927. For 2-center, 2-electron chemical bonds, one forms a Heitler-London or valence-bond wavefunction by singlet spin coupling the two fragment unpaired electrons in their overlapping non-orthogonal Abstract:The generalized Heitler-London (GHL) theory provides a straightforward way to express the potential energy surface of H3 in terms of Coulomb and exchange energies which can be calculated either by perturbation theory or using the surface integral method (SIM). By applying the Rayleigh-Schrödinger perturbation theory, GHL theory for the quartet spin state of H3 is shown to yield One of the many reasons behind the unwillingness of chemists to explore VB theory as a qualitative theoretical tool is the apparent size of the CW basis set. For example, in the case of a 4e-4c system, a complete VB basis set includes just two HL CW’s but |lxu| dja| yxr| dbp| xip| amb| can| nae| hdk| rhp| vhr| svz| uhl| cjn| wmc| ebz| hdy| ykn| esl| pvg| okk| nnm| tkh| ggd| qxi| wzr| cby| jlv| oth| jgs| kbu| rpt| iab| iat| rtw| vif| ugj| jvx| rte| dtd| zud| mdk| nyp| dbs| fxm| jtl| kmb| vhq| qjm| azs|