Đang chuẩn bị liên kết để tải về tài liệu:
Ideas of Quantum Chemistry P42

Ideas of Quantum Chemistry P42 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. | 376 8. Electronic Motion in the Mean Field Atoms and Molecules The first and last functions are singlets Sz 0 S 0 while the second function represents a triplet state Sz 0 S 1 Appendix Q on p. 1006. Thus a small diversification of the orbital functions leads to some triplet second term and singlet third term admixtures to the original singlet function N N_ rhf called triplet contamination . The former is proportional to 5 and the latter to 52. Now the total wave function is no longer an eigenfunction of the S2 operator. How is this possible If one electron has a spin coordinate of 1 and the second one of -1 aren t they paired Well not necessarily because one of the triplet functions which describes the parallel configuration of both spins85 is a 1 2 a 1 2 . Is the resulting UHF energy calculated for such a function lower than the corresponding RHF energy calculated for RHF i.e. is the RHF solution unstable ASDW towards ASDW-type spinorbitals changes no. 4 in the Table of Fukutome classes It depends on a particular situation. A while before we promised to consider what the 5 function should look like for the hydrogen molecule. In the RHF method both electrons occupy the same molecular orbital p. If we assume within the UHF method that whenever one electron is close to the a nucleus the second one prefers to be closer to b this would happily be accepted by the electrons since they repel each other the mean value of the Hamiltonian would decrease this is welcome . Taking the 5 sp function where p is the antibonding orbital and s 0 is a small coefficient would have such consequences. Indeed the sum p 5 p sp takes larger absolute value preferentially at one of the nuclei86 Fig. 8.15 . Since both orbitals correspond to electrons with opposite spins there will be some net spin on each of the nuclei. This nicely justifies the name of Axial Spin Density Wave ASDW Fukutome gave to the UHF method. AMO method A similar reasoning pertaining function p - 5 p - sp results in .