Charge equilibration method

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... 

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 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,. . . ) ... 

The electronegativity equalisation method [30] and the charge equilibration method [31] were designed to introduce charges which depend on the atomic environment and the local electric field. The atomic charges predicted by these methods agree well with the experimental values and with the ones determined by quantum mechanical methods for ionic crystals and organic molecules. 

MD simulations with Dreiding 2.21 force field 200 ps charge equilibration method 8.5-A cut-off... 

UFF was originally designed to be used without an electrostatic term. The literature accompanying one piece of software recommends using charges obtained with the Q-equilibrate method. Independent studies have found the accuracy of results to be signihcantly better without charges. 

The Q-equilibrate method is applicable to the widest range of chemical systems. It is based on atomic electronegativities only. An iterative procedure is used to adjust the charges until all charges are consistent with the electronegativities of the atoms. This is perhaps the most often used of these methods. 

For molecular mechanics, the charge calculation method used in parameterizing the force field should be used if possible. Otherwise, use Q-equilibrate or electrostatic charges. 

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... 

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... 

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. 

Small-scale supercritical extractions may be either dynamic or static. If the fluid is pumped through the sample chamber continuously, then the method is dynamic. If the sample container is filled batchwise with pressurized fluid, then the method is static. In the latter case, the sample container is charged, equilibrated statically, and then discharged through a throttle to collect the residue as before. In either case, the pressurized fluid or solvent is not recycled, and this feature limits the applicability to industrial use, because solvent costs, even with recycle, often determine whether or not extraction is economical. 

The more usual method of formation is to completely assemble the battery, fill it with electrolyte, and then apply the formation charge. This method is used for SLI and most stationary and traction batteries. A variety of formation conditions are used, similar to those for tank formation. The two major formation processes are the two-shot formation process (used for stationary and traction batteries) and the one-shot formation process (used for most SLI batteries). In the two-shot formation, the electrolyte is dumped to remove the low-density initial electrolyte and refilled with more concentrated electrolyte, chosen so that when this is mixed with the dilute initial acid residue which is absorbed in the elements or trapped in the case, the cell electrolyte will equilibrate at the desired density (Table 23.11). Typical values of the electrolyte specific gravity at full charge after formation are given in Table 23.12. 

The formalism of the fluctuating charge model is based on the charge equilibration (CHEQ) method," in which the chemical potential is equilibrated via... 

T. Ogawa, N. Kurita, H. Sekino, O. Kitao, and S. Tanaka, Chem. Phys. Lett., 397(4-6), 382-387 (2004). Consistent Charge Equilibration (CQEQ) Method Application to Amino Acids and Crambin Protein. 

---