First principles simulations of high

Predictions of high explosive detonation based on the new approach yield excellent results. A similar theory for ionic species model43 compares very well with MD simulations. Nevertheless, high explosive chemical equilibrium calculations that include ionization are beyond the current abilities of the Cheetah code, because of the presence of multiple minima in the free energy surface. Such calculations will require additional algorithmic developments. In addition, the possibility of partial ionization, suggested by first principles simulations of water discussed below, also needs to be added to the Cheetah code framework. 

First-principles simulations of one- or few-electron systems involve quantum systems of the lowest dimensionality we will consider in this section. These might entail the smallest error intrinsic in the calculation of the wave function. However, the blessing of small dimensionality is compensated by the tendency of systems in this class usually involve electrons in highly irregular potentials. Furthermore, the potential is usually a pseudopotential which describes the effect of atomic cores and/or solvent molecules on the quantum system of interest. Unfortunately, pseudopotentials introduce errors which are difficult to calibrate. 

The combination of state-of-the-art first-principles calculations of the electronic structure with the Tersoff-Hamann method [38] to simulate STM images provides a successful approach to interpret the STM images from oxide surfaces at the atomic scale. Typically, the local energy-resolved density of states (DOS) is evaluated and isosurfaces of constant charge density are determined. The comparison between simulated and measured high-resolution STM images at different tunneling... 

The greatest limitation of QC methods is computational expense. This expense restricts system sizes to a few hundred atoms at most, and hence, it is not possible to examine highly elaborate systems with walls that are several atomic layers thick separated by several lubricant atoms or molecules. Furthermore, the expense of first-principles calculations imposes significant limitations on the time scales that can be examined in MD simulations, which may lead to shear rates that are orders of magnitude greater than those encountered in experiments. One should be aware of these inherent differences between first-principles simulations and experiments when interpreting calculated results. 

Due to their localized nature, core electrons can only be adequately described with G - vectors of very high frequency, which would necessitate the use of prohibitively large basis sets in a standard plane wave scheme. Consequently, only valence electrons are treated explicitly and the effect of the ionic cores is integrated out using a pseudopotential formalism. Consistent with the first-principles character of Car-Parrinello simulations, the pseudopotentials used for this purpose are ab initio pseudopotentials (AIPPs). AIPPs are derived directly fixnn atomic all-electron calculations and different schemes exist for their construction. One of the general... 

A comparison of the predictions for the cavity pair correlation function of some first-principles theories with computer simulation results [72] at a fairly high density has been presented by Stell (see Fig. 2 in Ref. 69). The... 

The ring-opening mechanism was well supported by the snapshots and the overlap bond population obtained from TB-QCMD simulations, where the formation of new C-H and La-C bonds and the dissociation of La-H and proximal C-C bonds could be tracked. The obtained dynamic ring opening mechanism was similar to the static mechanism, however, a novel transition state was also proposed for insertion reaction of alkenes, with tetrahedral h4-coordination. This example perfectly illustrates the importance of mutual interplay between high-level first principle methodologies and simplified methodologies derived from ab initio quantum chemistry, massively applicable for real systems. 

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