IMOMO method

S. Flumbel, S. Sieber and K. Morokuma, The IMOMO method Integration of different levels of molecular orbital approximations for geometry optimization of large systems test for n-butane conformation and s(n)2 reaction RC1 + C1, J. Chem. Phys., 105 (1996) 1959-1967. 

Table 1 Activation Barriers a(kcal mol ) for the Diels-Alder Addition of Acetylenedicarboxylic Acid with Cyclopentadiene. Various IMOMO Methods are Shown and Model Predictions for HF, MP2, MP4, and G2MS are Given, as are the Size Corrections for Real Model at the HF and MP2 Levels and the Method Corrections for the Model at G2MS HF and G2MS MP2...

Table 2 Activation Barriers (kcal mol ) for a Series of Diels - Alder Additions. The IMOMO Method has been Used and the Model is Ethylene -I- Butadiene. The High level Model Prediction is at the G2MS CCSD(T)/6-31G + MP2/6-311-hG(2df,2p) - MP2/6-31G Level and the Low Level Real Predictions are at the MP2 Level of Theory...

Three such methods have been proposed by Morokuma and coworkers. The integrated MO + MM (IMOMM) method combines an orbital-based technique with an MM technique. The integrated MO + MO method (IMOMO) integrates two different orbital-based techniques. The our own n-layered integrated MO and MM method (ONIOM) allows for three or more different techniques to be used in successive layers. The acronym ONIOM is often used to refer to all three of these methods since it is a generalization of the technique. 

Froese, R. D. J., Humbel, S., Svensson, M., Morokuma, K., 1997, IMOMO(G2MS) A New High-Level G2-like Method for Large Molecules and Its Application the Diels-Alder Reactions , J. Phys. Chem. A, 101, 227. 

T. Vreven and K. Morokuma, On the application of the IMOMO (integrated molecular orbital + molecular orbital) method, J. Comput. Chem., 21 (2000) 1419-1432. 

Clearly, obtaining an ab initio description of a system as large as this with a reasonable basis set is an unrealistic undertaking. Thus we have chosen to use the layering method (IMOMO) of Morokuma and coworkers [38], in which the full system is divided into three sets with coordinates denoted by Ru R2 and R3, respectively. 

The IMOMM (integrated molecular orbital plus molecular mechanics) method resembles IMOMO, but the lower level used is the molecular-mechanics method (Section 16.6) and some details of the implementation differ from IMOMO [F. Maseras and K. Morokuma,/. Comput. Chem., 16,1170 (1995)]. 

The IMOHC (integrated molecular orbital method with harmonic cap) method is a modification of IMOMO and IMOMM in which the bond distances to the link atom in the real system and the capping atom in the model system are not frozen but are allowed to vary in the optimization [J. C. Corchado and D. G. Truhlar, J. Phys. Chern.A,m,ms 1998)1... 

The ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) method is an extension of IMOMO and IMOMM that performs calculations on n different systems using n levels of calculation. Each system and calculation level constitute a layer. The IMOMO and IMOMM methods are versions of ONIOM with n = 2. ONIOM3 is the three-layered version of ONIOM and uses a real system calculated at a low level, an intermediate model system calculated at a medium level, and a small model system calculated at a high level [M. Svensson et al., J. Phys. Chem., 100,19357 (1996)]. 

IMOMO (Integrated Molecular Orbital Plus Molecular Orbital) Method. 

Bazilevskii, M. V. Molecular Orbitals Method and Reaction Ability of Organic Molecules. Moscow, Khimia 1969 Vreven, T. Morokuma, K. The accurate calculation and prediction of the bond dissociation energies in a series of hydrocarbons using the IMOMO. (integrated molecular orbital-emolecular orbital) methods. Journal of Chem. Phys. 1999, 111(19), 8799-8803. 

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