Quantum mechanical molecular electrostatic potentials

The applications of NN to solvent extraction, reported in section 16.4.6.2., suffer from an essential limitation in that they do not apply to processes of quantum nature therefore they are not able to describe metal complexes in extraction systems on the microscopic level. In fact, the networks can describe only the pure state of simplest quantum systems, without superposition of states. Neural networks that indirectly take into account quantum effects have already been applied to chemical problems. For example, the combination of quantum mechanical molecular electrostatic potential surfaces with neural networks makes it possible to predict the bonding energy for bioactive molecules with enzyme targets. Computational NN were employed to identify the quantum mechanical features of the... 

In MM3 the option exists to compute charge-charge and charge-dipole interaction energies between ions and between ions and polar molecules. The values for the bond dipoles were chosen to reproduce the molecular dipole moments for test molecules. It has been demonstrated that bond dipoles may be derived to reproduce the quantum mechanical molecular electrostatic potential (ESP) and that a dipole model can perform as effectively as the more common partial atomic charge model derived from the same potential.The... 

It is worth to remark that the opposite also happens. There is an evolution in the experimental teehniques too, and in some eases this progress makes possible ( or competitive) the measurement of a quantity formerly available via computations only. One example is the detailed measurement of the electronic density of a molecule, and of the related molecular electrostatic potential. The determination of these two observables has been for many years a task feasible only by quantum-mechanical methods, now the progresses in the elaboration of diffraction technique measurements makes possible a direct determination. 

A more sophisticated way to look at charge distribution is the molecular electrostatic potential energy map of the reactant(s). Programs like SPARTAN can compute and display the MEP of a molecule as part of its quantum mechanical repertoire. In an alternate visualization of the MEP, it is common for such graphics programs to display the electron... 

The molecular electrostatic potential (MEP) is a rigorously defined quantum mechanical property. The electrostatic potential (EP) at a point r in the... 

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. 

Aguilar, Sanchez, Martin, Fdez. Galvan review the ASEP/MD method, acronym for Averaged Solvent Electrostatic Potential from Molecular Dynamics, showing how this method combines aspects of quantum mechanics/molecular mechanics (QM/MM) methods with aspects of continuum models. 

In Figure 3.1, we present the RMSD obtained by a comparison between the molecular electrostatic potential due to multipole moments taken from the considered force fields and the quantum mechanically computed potential for different distances from the molecular van der Waals surface. From Figure 3.1, it is clearly demonstrated that the multipole expansion is appropriate at large distances from the molecule and that higher order multipoles are mandatory to consider when the molecular potential close to the... 

In this approximation, the system is modeled by calculating the appropriate surface charges at the dielectric boundary. This is similar to fitting charges at atomic centers to reproduce the molecular electrostatic potential. For a quantum-mechanical equivalent, Tomasi et al. (59) introduced a charge distribution on the surface of a cavity of realistic shape to introduce... 

Keywords alchemical free energy simulation combined quantum mechanical/ molecular mechanical potential generalized ensemble simulation conformational sampling long-range electrostatic interaction... 

Molecular electrostatic potential The molecular electrostatic potential (MEP) associated with a molecule arises from the distribution of electrical charges of the nuclei and electrons of a molecule. The MEP is quantum mechanically defined in terms of the spatial coordinates of the charges on the nuclei and the electronic density function p(r) of the molecule. As the MEP is the net result of the opposing effects of the nuclei and the electrons, electrophiles will be guided to the regions of a molecule where the MEP is most negative. The MEP is a useful quantity in the study of molecular recognition processes. 

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