Ideas of Quantum Chemistry P18 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 136 3. Beyond the Schrödinger Equation The term p4 and the total Darwin effect nearly cancel each other for unclear reasons. This cancellation is being persistently confirmed also in other systems. Mysteriously enough this pertains not only to the ionization energy but also to the polarizability. After the above mentioned cancellation of p4 and Darwin terms retardation becomes one of the most important relativistic effects. As seen from the Table the effect is about a 100 times larger both for the ionization energy and the polarizability for the electron-electron retardation than for that of the nucleuselectron. This is quite understandable because the nucleus represents a massive rock it is about 7000 times heavier in comparison to an electron it moves slowly and in the nucleus-electron interaction only the electron contributes to the retardation effect. Two electrons make the retardation much more serious. Term 3 spin-orbit coupling is equal to zero for symmetry reasons for the ground state . In the Darwin term the nucleus-electron vs electron-electron contribution have reversed magnitudes about 1 10 as compared to 100 1 in retardation . Again this time it seems intuitively correct. We have the sum of the particle-particle terms in the Hamiltonian 4 .2 2 E o P2 E r2 where E means an electric field created by two other particles on the particle under consideration. Each of the terms is proportional to VjVjV A V 4nq 5 r where 5 is the 5 Dirac delta function Appendix E p. 951 and q denotes the charge of the particle i . The absolute value of the nuclear charge is twice the electron charge. In term 5 the spin-spin relates to the electron-electron interaction because the helium nucleus has spin angular momentum of 0. The Coulombic interactions are modified by the polarization of vacuum similar to the weaker interaction of two charges in a dielectric medium . Table reports such corrections46 to the electron-electron and the electron-nucleus interactions QED c-3 .
