Charge equilibration

Rappe A K and W A Goddard III 1991. Charge Equilibration for Molecular Dynamics Simulations. Journal of Physical Chemistry 95 3358-3363. 

Rappe AK, Goddard WA (1991) Charge equilibration for molecular-dynamics simulations. J Phys Chem 95(8) 3358-3363... 

Kitao O, Ogawa T (2003) Consistent charge equilibration (CQEq). Mol Phys 101(1—2) 3—17... 

Nistor RA, Polihronov JG, Muser MH, Mosey NJ (2006) A generalization of the charge equilibration method for nonmetallic materials. J Chem Phys 125(9) 094108... 

Ogawa T, Kurita N, Sekino H, Kitao O, Tanaka S (2004) Consistent charge equilibration (CQEq) method application to amino acids and crambin protein. Chem Phys Lett 397(4-6) 382-387... 

Sefcik J, Demiralp E, Cagin T, Goddard WA (2002) Dynamic charge equilibration-morse stretch force field application to energetics of pure silica zeolites. J Comput Chem 23(16) 1507-1514... 

Tanaka M, Siehl HU (2008) An application of the consistent charge equilibration (CQEq) method to guanidinium ionic liquid systems. Chem Phys Lett 457(1—3) 263—266... 

The return to equilibrium of a polarized region is quite different in the Debye and Lorentz models. Suppose that a material composed of Lorentz oscillators is electrically polarized and the static electric field is suddenly removed. The charges equilibrate by executing damped harmonic motion about their equilibrium positions. This can be seen by setting the right side of (9.3) equal to zero and solving the homogeneous differential equation with the initial conditions x = x0 and x = 0 at t = 0 the result is the damped harmonic oscillator equation ... 

Another Class I charge model that is also sensitive to geometry is the QEq charge equilibration model of Rappe and Goddard (1991). From representing the energy m of an isolated atom k as a Taylor expansion in its charge truncated at second order, one can derive... 

The formaldehyde dynamics ran for 25ps, with a time step of 0.1 fs. Figure 1.9 reports the results obtained with the charges equilibrated at each step and with the extended... 

Figure 1.9 Total and potential energy (au) of formaldehyde in water, (a) with the PCM charges equilibrated at each time step and (b) with the PCM extended Lagrangian formulation.

As for hybrid modeling, the problem of the foundations of MM is seen from a somewhat different perspective. A priori there is no limitation for employing that or any other MM scheme as a classical component of a hybrid model. In practice, however, different MM schemes behave differently when tailored to a QM treated part. Indeed, it is not clear how to handle the bond-dipole based electrostatic energy employed in the MM2 and MM3 schemes, if some bond must be broken, as their ends are expected to be treated by different methods. It applies even more to the schemes with charge equilibration. We shall try to describe the problems created by these inconsistencies as related to the current hybrid methods in the next section, with the analysis of the current state of the art, from the point of view of the general theory of electron variables separation. 

Rappe, A.K. and Goddard, W.A., Charge equilibration for molecular dynamics simulation, J. Phys. Chem.,... 

The amorphous nucleation layer has the consequence that the Fermi level of the growing ZnO films reaches its equilibrium value already at very low thickness ( 2nm). This is particularly important for ZnO Al films, where the Fermi level changes by more than 1 eV upon the addition of oxygen to the sputter gas. The amorphous nucleation layer, therefore, substitutes the space charge layer, which is usually necessary for charge equilibration at the interface. This important effect is illustrated in Fig. 4.25. 

Surface states can arise simply because the atomic bonding at a semiconductor surface is necessarily different from that in the bulk. For example, in a Si lattice, the bonds at the Si surface are not ftilly coordinatively saturated. To relieve this unsaturation, either a surface reconstruction can occur and/or bonds to the metallic material can be formed. This distinct type of surface bonding results in a localized electronic structure for the surface which is different from that in the bulk. The energies of these localized surface orbitals are not restricted to reside in the bands of the bulk material, and can often be located at energies that are inside the band gap of the semiconductor. Orbitals that reside in this forbidden gap region are particularly important, because they will require modifications of our ideal model of charge equilibration at semiconductor/metal interfaces. ... 

Cerius2 (MSI Inc.) was used throughout the simulations. Adsorption equilibria was carried out by GCMC method for same systems of experiments. Adsorbent model was pure silicious Y type that was same type as experimental adsorbent. Simulation forcefield parameters were new forcefield parameter obtained by Mellot et al l Solvent charges were determined with Charge-Equilibration method, respectively. 

A novel approach based on the concept of charge equilibration has been suggested by Rappe and Goddard (84)that allows the inclusion of polarizabilities in molecular dynamics calculations. 

A model related to EEM has been proposed by Rappe and Goddard and is called the charge equilibration method (QEq). The main difference between EEM and QEq lies in the treatment of the electrostatic interactions. In EEM these interactions are calculated using the point charge approximation assuming a 1/r dependence for the interaction energy, whereas in QEq the interactions are calculated between ns Slater orbitals (n = 1, 2,. . . ) ... 

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