ONIOM方法原理介绍.PPT

Gauge Invariant Atomic Orbital (GIAO) method: a particularly accurate method for NMR parameter calculations Two-layer ONIOM(MP2-GIAO:HF-GIAO) scheme, Karadakov et al. used the following expression to calculate ONIOM isotropic NMR chemical shieldings: This method was applied to calculate absolute isotopic (13C,?17O, and?19F) proton NMR chemical shieldings in the water dimer, ethanol, acetone, acrolein, fluorobenzene, and naphthalene. ONIOM(MP2-GIAO:HF-GIAO) was consistent with the full MP2-GIAO results. The ONIOM method has also been applied to compute accurate NMR chemical shifts of a number of systems ONIOM Methods: Molecular Properties 2 Nuclear Magnetic Resonance   ONIOM Methods: Molecular Properties 2 ONIOM Energy Decomposition Analysis ?Investigate the electronic effects as well as steric effects of substituents ONIOM(QM:MM) for the real system decompose the substituent effects into steric and electronic effects ONIOM(QM:QM) for the real system) high-level QM model system ONIOM Methods: Geometry Optimization 2 Geometry Optimization and Microiteration Methods ONIOM uses an efficient hybrid optimization method First, a complete geometry optimization of the environment system is performed with MM, with the fixed model system (microiterations). Second, perform one expensive QM optimization step of the small model system with the entire environment system fixed (macroiterations). This process is repeated until atomic forces of the whole system converge to some specific threshold. Such separate geometry optimization method: Reduce the number of the expensive QM calculations, Make use of two different and efficient optimization methods: small model system: a memory-demanding second-order algorithm (e.g., the Newton–Raphson (NR) or rational function optimization (RFO) in redundant internal coordinates) ; large environment system: a first-order algorithm (e.g., steepest descent or conjugate gradient optimization in Cartesian coordinates) . * *