Quantum mechanical/molecular mechanics QM/MM simulation

The equations written down at the beginning of this section are formally the same as the equations used in quantum mechanical/molecular mechanical (QM/MM) simulations, but only applied to the much simpler system of a 2LS coupled to a classical oscillator. In QM/MM simulations, but also in equilibrium calculations the effect of environmental polari2ation is taken into account by selfelectronic states of the molecule in interaction with an environment that adjusts its polarization to the electric fields generated by the environment in equilibrium with the (expectation value of) the electronic density and the positions of the nuclei. As we have indicated before, there is nothing wrong with Eq. (9.53). The electric field E(t) experienced by the enol-keto system is just a classical field acting on the quantum states, and this does not lead to inconsistencies. The... 

Abstract A mixed molecular orbital and valence bond (MOVB) method has been developed and applied to chemical reactions. In the MOVB method, a diabatic or valence bond (VB) state is defined with a block-localized wave function (BLW). Consequently, the adiabatic state can be described by the superposition of a set of critical adiabatic states. Test cases indicate the method is a viable alternative to the empirical valence bond (EVB) approach for defining solvent reaction coordinate in the combined quantum mechanical and molecular mechanical (QM/MM) simulations employing explicit molecular orbital methods. 

Bioinformatic tools are of increasing importance for the characterization of flavoenzymes. This finding holds for protein sequence and protein structural analysis as well as for gaining insight into the reactivity of the flavin cofactor by combined quantum mechanical and molecular mechanical (QM/MM) simulations (12). 

A widely used type of multiscale simulation combines quantum mechanical and molecular mechanical (QM/MM) simulations. In this approach, the functional core of the molecular system, for example, the catalytic sites of an enzyme, is described at the electronic level (QM region), whereas the surrounding macromolecular system is treated using a classical description (MM region). Some of the biological applications for which QM/MM calculations have been widely utilized are chemical reactions in enzymes, proton transfer in proteins and optical excitations. In QM/MM... 

Acevedo O, Jorgensen WL (2010) Advances in quantum and molecular mechanical (QM/ MM) simulations for organic and enzymatic reactions. Acc Chem Res 43 142-151... 

Acevedo O, Jorgensen WL (2010) Advances in quantum and molecular mechanical (QM/ MM) simulations for organic and enzymatic reactions. Acc Chem Res 43 142-151 Bands P, Jurecka P, Walter NG, Sponer J, Otyepka M (2009) Theoretical studies of RNA catalysis hybrid QM/MM methods and their comparison with MD and QM. Methods 49 202... 

A Fortran90 library for the simulation of molecular systems using molecular mechanics (MM) and hybrid quantum mechanics/molecular mechanics (QM)/ MM) potential energy functions. http //www.ibs.fr/ext/labos/LDM/projet6/... 

Despite advent of theoretical methods and techniques and faster computers, no single theoretical method seems to be capable of reliable computational studies of reactivities of biocatalysts. Ab initio quantum mechanical (QM) methods may be accurate but are still too expensive to apply to large systems like biocatalysts. Semi-empirical quantum methods are not as accurate but are faster, but may not be fast enough for long time simulation of large molecular systems. Molecular mechanics (MM) force field methods are not usually capable of dealing with bond-breaking and formation... 

In our simulations of histone modifying enzymes, the computational approaches centered on the pseudobond ab initio quantum mechanical/molecular mechanical (QM/MM) approach. This approach consists of three major components [20,26-29] a pseudobond method for the treatment of the QM/MM boundary across covalent bonds, an efficient iterative optimization procedure which allows for the use of the ab initio QM/MM method to determine the reaction paths with a realistic enzyme environment, and a free energy perturbation method to take account... 

In addition to the described above methods, there are computational QM-MM (quantum mechanics-classic mechanics) methods in progress of development. They allow prediction and understanding of solvatochromism and fluorescence characteristics of dyes that are situated in various molecular structures changing electrical properties on nanoscale. Their electronic transitions and according microscopic structures are calculated using QM coupled to the point charges with Coulombic potentials. It is very important that in typical QM-MM simulations, no dielectric constant is involved Orientational dielectric effects come naturally from reorientation and translation of the elements of the system on the pathway of attaining the equilibrium. Dynamics of such complex systems as proteins embedded in natural environment may be revealed with femtosecond time resolution. In more detail, this topic is analyzed in this volume [76]. 

Mixed Quantum Mechanical/Molecular Mechanical (QM/MM) Car-Parinello Simulations... 

From its inception, the combined Quantum Mechanics/Molecular Mechanics (QM/MM) method [1-3] has played an important roll in the explicit modeling of solvent [4], Whereas Molecular Mechanics (MM) methods on their own are generally only able to describe the effect of solvent on classical properties, QM/MM methods allow one to examine the effect of the solvent on solute properties that require a quantum mechanical (QM) description. In most cases, the solute, sometimes together with a few solvent molecules, is treated at the QM level of theory. The solvent molecules, except for those included in the QM region, are then treated with an MM force field. The resulting potential can be explored using Monte Carlo (MC) or Molecular Dynamics (MD) simulations. Besides the modeling of solvent, QM/MM methods have been particularly successful in the study of biochemical systems [5] and catalysis [6],... 

The ASEP/MD method, acronym for Averaged Solvent Electrostatic Potential from Molecular Dynamics, is a theoretical method addressed at the study of solvent effects that is half-way between continuum and quantum mechanics/molecular mechanics (QM/MM) methods. As in continuum or Langevin dipole methods, the solvent perturbation is introduced into the molecular Hamiltonian through a continuous distribution function, i.e. the method uses the mean field approximation (MFA). However, this distribution function is obtained from simulations, i.e., as in QM/MM methods, ASEP/MD combines quantum mechanics (QM) in the description of the solute with molecular dynamics (MD) calculations in the description of the solvent. 

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