Plane waves recent studies

The study of the enantioselective hydrosilylation reaction was performed with a series of combined quantum mechanics/molecular mechanics (QM/MM) calculations [26, 30] within the computational scheme of ab initio (AIMD) (Car-Parrinello) [62] molecular dynamics. The AIMD approach has been described in a number of excellent reviews [63-66], AIMD as well as hybrid QM/MM-AIMD calculations [26, 47] were performed with the ab initio molecular dynamics program CPMD [67] based on a pseudopotential framework, a plane wave basis set, and periodic boundary conditions. We have recently developed an interface to the CPMD package in which the coupling with a molecular mechanics force field has been implemented [26, 68],... 

A recent study of the role of Al in expl mixts is that of Cook and co-workers(Ref 42). The low relative "brisance of aluminized explosives has been attributed in the past to incomplete reaction of Al at the Chapman -Jouguet plane," and the high blast potential to after-burning of the Al. Thus, early shaped charge studies indicated that Al acts effectively as a diluent as far as the end effect is concerned. More careful studies by Cook showed, however, that Al lowers the detonation pressure and velocity even more than an ideal diluent. The effective endothermic reaction of Al in the deto n wave is shown in the following results of deton pressures measured by the shaped charge method ... 

For the purposes of this review it is convenient to focus attention on that class of molecules in which the valence electrons are easily distinguished from the core electrons (e.g., -n electron systems) and which have a large number of vibrational degrees of freedom. There have been several studies of the photoionization of aromatic molecules.206-209 In the earliest calculations either a free electron model, or a molecule-centered expansion in plane waves, or coulomb functions, has been used. Only the recent calculation by Johnson and Rice210 explicitly considered the interference effects which must accompany any process in a system with interatomic spacings and electron wavelength of comparable magnitude. The importance of atomic interference effects in the representation of molecular continuum states has been emphasized by Cohen and Fano,211 but, as far as we know, only the Johnson-Rice calculation incorporates this phenomenon in a detailed analysis. 

Ilyukhin Pokhil (Ref 5) used plane wave shocks thru a brass barrier to initiate RDX. For RDX of MJ.lmm particle size at 1.74g/cc the threshold shock was found to be lSkbai A recent study by Dremin Shvedov (Ref 99) examined the effect of gas additives on the shock initiation of RDX and TNT lightly pressed charges of po M g/cc.The nature of the gas or its partial press had no effect. They did find an interesting effect in all their observations, namely a break in the plot of barrier/expl interface velocity (u) vs time. Their summary plot for RDX is shown in Fig 5... 

New calculations using a more efficient CRYSTAL code [54] and optimization scheme [135] are presented here. In these, also the spin-polarized B3LYP hybrid functional was used and the orthorhombic structure of Li05TiO2 was studied. The same basis set was used as in [66]. Recently, the orthorhombic Li0.5TiO2 structure was studied by plane-wave generalized gradient-approximation (GGA) DFT calculations by Koudriachova et al. [136]. GGA calculations were performed also in the present study for comparison. 

The overwhelming majority of the theoretical studies were performed on cluster models of the catalytic site, hi spite of the fact that the role of space confinement and the secondary interactions with the framework atoms is well-known, there are only a few electronic structure calculations on lattice models involving hydrocarbons, using either periodic DFT calculations, or embedding methods. In this brief account of the subject we attempt to overview some of the recent computational results of the literature and present some new data obtained from ab initio DFT pseudopotential plane wave calculations on Cl - C4 alkanes in the chabazite framework. 

In fact, because of its importance in solid-state science, a large variety of band-structure approaches have been used to calculate the electronic structure of sphalerite. These have included self-eonsistent and semiem-pirical orthogonalized-plane-wave (OPW) (Stukel et al., 1969), empirical-pseudopotential (Cohen and Bergstresser, 1966), tight-binding (Pantelides and Harrison, 1975), APW (Rossler and Lietz, 1966), and modified OPW (Farberovich et al., 1980), as well as KKR (Eckelt, 1967) methods. In a recent and extremely detailed study using a density-functional approach (specifically a method termed the self-consistent potential variation... 

Solution of the Kohn-Sham equations as outlined above are done within the static limit, i.e. use of the Born-Oppenheimer approximation, which implies that the motions of the nuclei and electrons are solved separately. It should however in many cases be of interest to include the dynamics of, for example, the reaction of molecules with clusters or surfaces. A combined ab initio method for solving both the geometric and electronic problem simultaneously is the Car-Parrinello method, which is a DFT dynamics method [52]. This method uses a plane wave expansion for the density, and the inner ions are replaced by pseudo-potentials [53]. Today this method has been extensively used for studies of dynamic problems in solids, clusters, fullerenes etc [54-61]. We have recently in a co-operation project with Andreoni at IBM used this technique for studying the existence of different isomers of transition metal clusters [62,63]. 

The band structures of the transition metal monoxides including NiO have been a topic of considerable interest for many years, and study of spectra and transport properties continues in an effort to determine band widths, separations and electrostatic correlation energies. NiO is a Mott insulator (96) and the localized electron description assumed here is probably appropriate. Augmented plane wave band structure calculations have recently been made for NiO and other monoxides (97) and a localized electron multiple scattering Xa calculation for NiO (98). Neither type of calculation includes electron-electron correlation effects. 

A recent study [93JCS(D)967] of aryl-l,3,2,4-dithiadiazoIylium salts has shown that they typically show a half-wave reduction potential in the region +0.29 Em < +0.4 V (with reference to the standard calomel electrode). As found for the 1,2,3,5-isomers, these salts show a Hammett relationship between 1/2 and the a value for the para substituent on the aryl group. The greater reaction constant p, for the 3+/3 redox system, compared with 2+/2, is in agreement with MO calculations—which indicate some unpaired spin density on the heterocyclic carbon, allowing delocalization onto the aryl substituent. (The nodal plane associated with 2 prohibits, to a first-order approximation, delocalization with the aryl functionality.)... 

Other codes came later. One was the implementation of DFT in the well-known CRYSTAL code [61], already mentioned. Originally CRYSTAL was a Hartree-Fock package. Suppported by a large development collaboration, CRYSTAL is widely distributed and has a much more user-friendly interface than GTOFF. At least with default settings and basis sets, however, CRYSTAL appears to give peculiar results sometimes. The most recent example is a predicted double min-imiun for the a-quartz equilibrium structure at very different molar volumes per formula unit [62]. No other DFT study of a-quaitz equilibrium had found this behavior, but they were all plane-wave/pseudopotential or cellular basis. We do not find it either [63]. See discussion below. 

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