Multiconfigurational molecular mechanics

T. V. Albu, J. C. Corchado, D. G. Truhlar, J. Phys. Chem. A 105, 8465 (2001). Molecular Mechanics for Chemical Reactions A Standard Strategy for Using Multiconfiguration Molecular Mechanics for Variational Transition State Theory with Optimized Multidimensional Tunneling. 

Other approaches to model transition states with force fields are the empirical valence bond model (EVB). [336] the reactive force field (RFF) [337] and the multiconfigurational molecular mechanics (MCMM) method [338]. 

Higashi M, Truhiar DG (2008) Electrostatically embedded multiconfiguration molecular mechanics based on the combined density functional and molecular mechanical method. J Chem Theory Comput 4 790-803... 

VB (BOVB) method, which also utilizes covalent and ionic structures, but in addition allows them to have their own unique set of orbitals. This method is now incorporated into the programs TURTLE and XIAMEN-99. Very recently, Wu et al. developed a VBCI method that is akin to BOVB, but which can be applied to larger systems. The recent biorthogonal VB method (bio-VB) of McDouall has the potential to carry out VB calculations on systems with up to 60 electrons outside the closed shell. And finally, Truhlar and co-workers " ° developed the VB-based multiconfiguration molecular mechanics method (MCMM) to treat dynamical aspects of chemical reactions, while Landis and co-workers " introduced the VAL-BOND method that predicts the structures of transition metal complexes using Pauling s ideas of orbital hybridization. In the section dedicated to VB methods, we mention the main software and methods that we used, and outline their features, capabilities, and limitations. 

Mechanics for Chemical Reactions A Standard Strategy for Using Multiconfiguration Molecular Mechanics for Variational Transition State Theory with Optimized Multidimensional Tunneling. 

Multiconfiguration Molecular Mechanics Algorithm for Potential Energy Surfaces of Chemical Reactions. 

Albu TV, Corchado JC, Truhlar DG (2001) Molecular mechanics for chemical reactions a standard strategy for using multiconfiguration molecular mechanics for variational transition state theory with optimized multidimensional tunneling. J Phys Chem A 105 8465-8487... 

MULTICONFIGURATIONAL SELF-CONSISTENT FIELD-MOLECULAR MECHANICS RESPONSE METHODS... 

Keywords Multiconfigurational self-consistent field molecular mechanics response methods,... 

The present contribution concerns an outline of the response tlieory for the multiconfigurational self-consistent field electronic structure method coupled to molecular mechanics force fields and it gives an overview of the theoretical developments presented in the work by Poulsen et al. [7, 8, 9], The multiconfigurational self-consistent field molecular mechanics (MCSCF/MM) response method has been developed to include third order molecular properties [7, 8, 9], This contribution contains a section that describes the establisment of the energy functional for the situation where a multiconfigurational self-consistent field electronic structure method is coupled to a classical molecular mechanics field. The second section provides the necessary background for forming the fundamental equations within response theory. The third and fourth sections present the linear and quadratic, respectively, response equations for the MCSCF/MM response method. The fifth 283... 

Multiconfigurational Self-Consistent Field-Molecular Mechanics... 

Using the multiconfigurational approach combined with classical or molecular mechanics treatment of the environment a CASPT2//CASSCF/MM protocol was established (the // separator has the same meaning as above). Thus geometry optimization and molecular dynamics simulations are carried out at the CASSCF/MM level (this notation indicates that... 

Coupling of quantum mechanical molecular subsystems with larger classically treated subsystems has traditionally involved electronic structure models describing molecules embedded in a dielectric medium and this is a research area that has expanded tremendously over the last three decades [2-36]. Most of this work has involved electronic structure methods that have been based on uncorrelated electronic structure methods [2-12,15-19]. Accurate description of the electronic structure of molecular systems requires that the correlated electronic motion in the molecule is incorporated and therefore a number of correlated electronic structure methods have been developed such as the second order Moller-Plesset (MP2) [28,30,90,91], the multiconfigurational self-consistent reaction field (MCSCRF) [13,20] and the coupled-cluster self-consistent reaction field (CCSCRF) method [36]. 

The molecular orbital (MO) is the basic concept in contemporary quantum chemistry. " It is used to describe the electronic structure of molecular systems in almost all models, ranging from simple Hiickel theory to the most advanced multiconfigurational treatments. Only in valence bond (VB) theory is it not used. Here, polarized atomic orbitals are instead the basic feature. One might ask why MOs have become the key concept in molecular electronic structure theory. There are several reasons, but the most important is most likely the computational advantages of MO theory compared to the alternative VB approach. The first quantum mechanical calculation on a molecule was the Heitler-London study of H2 and this was the start of VB theory. It was found, however, that this approach led to complex structures of the wave funetion when applied to many-electron systems and the mainstream of quantum ehemistry was to take another route, based on the success of the central-field model for atoms introduced by by Hartree in 1928 and developed into what we today know as the Hartree-Foek (HF) method, by Fock, Slater, and co-workers (see Ref. 5 for a review of the HF method for atoms). It was found in these calculations of atomic orbitals that a surprisingly accurate description of the electronic structure could be achieved by assuming that the electrons move independently of each other in the mean field created by the electron cloud. Some correlation was introduced between electrons with... 

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