Đang chuẩn bị liên kết để tải về tài liệu:
Ideas of Quantum Chemistry P32

Ideas of Quantum Chemistry P32 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. | 276 7. Motion of Nuclei Anisotropy of the potential V Adding the angular momenta in quantum mechanics Application of the Ritz method Calculation of rovibrational spectra Force fields FF A Local molecular mechanics MM A Bonds that cannot break Bonds that can break p. 284 p. 290 Global molecular mechanics DC Multiple minima catastrophe Is it the global minimum which counts Small amplitude harmonic motion - normal modes A Theory of normal modes Zero-vibration energy Molecular dynamics MD A The MD idea What does MD offer us What to worry about MD of non-equilibrium processes Quantum-classical MD Simulated annealing A Langevin dynamics Monte Carlo dynamics A Car-Parrinello dynamics Cellular automata p. 292 p. 294 p. 304 p. 309 p. 310 p. 311 p. 314 p. 317 As shown in Chapter 6 the solution of the Schrödinger equation in the adiabatic approximation can be divided into two tasks the problem of electronic motion in the field of the clamped nuclei this will be the subject of the next chapters and the problem of nuclear motion in the potential energy determined by the electronic energy. The ground-state electronic energy E0 R of eq. 6.8 where k 0 means the ground state will be denoted in short as V R where R represents the vector of the nuclear positions. The function V R has quite a complex structure and exhibits many basins of stable conformations as well as many maxima and saddle points . The problem of the shape of V R as well as of the nuclear motion on the V R hypersurface will be the subject of the present chapter. It will be seen that the electronic energy can be computed within sufficient accuracy as a function of R only for very simple systems such as an atom plus a diatomic molecule for which quite a lot of detailed information can be obtained. In practice for large molecules we are limited to only some approximations to V R called force fields. After accepting such an approximation we encounter the problem of geometry optimization i.e. of obtaining the most stable