Electronic structure first-principle calculations

Anisimov V I, Aryasetiawan F and Liechtenstein A I 1997 First-principles calculations of the electronic structure and spectra of strongly correlated systems The LDA+U method J. Phys. Condens Matters 767... 

Yang, X. and Dong, J. (2005) Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations. Physical Review B -Condensed Matter, 71,233403-1-233403-4. 

The first-principles calculation of NIS spectra has several important aspects. First of all, they greatly assist the assignment of NIS spectra. Secondly, the elucidation of the vibrational frequencies and normal mode compositions by means of quantum chemical calculations allows for the interpretation of the observed NIS patterns in terms of geometric and electronic structure and consequently provide a means of critically testing proposals for species of unknown structure. The first-principles calculation also provides an unambiguous way to perform consistent quantitative parameterization of experimental NIS data. Finally, there is another methodological aspect concerning the accuracy of the quantum chemically calculated force fields. Such calculations typically use only the experimental frequencies as reference values. However, apart from the frequencies, NIS probes the shapes of the normal modes for which the iron composition factors are a direct quantitative measure. Thus, by comparison with experimental data, one can assess the quality of the calculated normal mode compositions. 

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... 

Qiu Guanzhou, Yu Runlan, Hu Yuehua, Qin Wenqing, 2004. Corrosive electrochemistry of jamesonite. Trans. Nonferrous Met. Soc. China, 14(6) 1169- 1173 Qiu Guanzhou, Xiao Qi, Hu Yuehua, 2004. First-principles calculation of the electronic structure of the stoichiometric pyrite FeS2(100) surface. Computation Materials Science, 03-11 ... 

The surface charge density of Al(lll) has been well characterized by first-principles calculations as well as helium scattering experiments. The asymptote of the corrugation amplitude Az of equal-LDOS surface contours follows an exponential law, as obtained from a first-principles calculation of the electronic structure of the Al(l 11) surface (Mednick and Kleinman, 1980) ... 

The importance and effect of tip electronic states were discussed by many authors (Tersoff, 1990 Tersoff and Lang, 1990 Doyen et al., 1990 Behm, 1990 Lawunmi and Payne, 1990 Sacks and Noguera, 1991). Doyen et al. (1990) made a first-principles calculation of a realistic W tip. They found that the electronic structure of the W tip exhibits a 54= resonance near the Fermi level, which is the most possible origin of atomic resolution. Sacks and Noguera (1991) noted that. v and d states dominate the DOS of the W surface near the Fermi level, and p states could arise from an adsorbed foreign atom. They have also derived the necessary formalism to account for the effect of p... 

The surface states observed by field-emission spectroscopy have a direct relation to the process in STM. As we have discussed in the Introduction, field emission is a tunneling phenomenon. The Bardeen theory of tunneling (1960) is also applicable (Penn and Plummer, 1974). Because the outgoing wave is a structureless plane wave, as a direct consequence of the Bardeen theory, the tunneling current is proportional to the density of states near the emitter surface. The observed enhancement factor on W(IOO), W(110), and Mo(IOO) over the free-electron Fermi-gas behavior implies that at those surfaces, near the Fermi level, the LDOS at the surface is dominated by surface states. In other words, most of the surface densities of states are from the surface states rather than from the bulk wavefunctions. This point is further verified by photoemission experiments and first-principles calculations of the electronic structure of these surfaces. 

The electron density distribution of a known surface structure can be calculated from first-principles. Thus, the He diffraction data can be compared with theoretical results, in particular, to verify different structural models. Hamann (1981) performed first-principles calculations of the charge-density distributions of the GaAs(llO) surface, for both relaxed and unrelaxed configurations. The He diffraction data are in excellent agreement with the calculated charge-density distributions of the relaxed GaAs(llO) surface, and are clearly distinguished from the unrelaxed ones (Hamann, 1981). 

The problem of first-principles calculations of the electronic structure of solid surface is usually formatted as a problem of slabs, that is, consisting of a few layers of atoms. The translational and two-dimensional point group symmetry further reduce the degrees of freedom. Using modern supercomputers, such first-principles calculations for the electronic structure of solid surfaces have produced remarkably reproducible and accurate results as compared with many experimental measurements, especially angle-resolved photoemission and inverse photoemission. 

The first successful first-principle theoretical studies of the electronic structure of solid surfaces were conducted by Appelbaum and Hamann on Na (1972) and A1 (1973). Within a few years, first-principles calculations for a number of important materials, from nearly free-electron metals to f-band metals and semiconductors, were published, as summarized in the first review article by Appelbaum and Hamann (1976). Extensive reviews of the first-principles calculations for metal surfaces (Inglesfeld, 1982) and semiconductors (Lieske, 1984) are published. A current interest is the reconstruction of surfaces. Because of the refinement of the calculation of total energy of surfaces, tiny differences of the energies of different reconstructions can be assessed accurately. As examples, there are the study of bonding and reconstruction of the W(OOl) surface by Singh and Krakauer (1988), and the study of the surface reconstruction of Ag(llO) by Fu and Ho (1989). 

If available, the LDOS at different energy levels, for the tip and the sample, is very useful information for predicting STM images. Several examples of surface electronic structures from first-principles calculations are reproduced as illustrations. 

Cutting across the domains of the various techniques mentioned above, are the model calculations l These are theoretical attempts to predict the structure of surfaces from first principles. The model calculations differ from the theories mentioned in conjunction with the experimental techniques listed above, in that the former are not primarily designed to describe the interaction of a probe with a surface, although obviously much overlap exists. Thus the calculation of electronic states at surfaces seeks to describe from first principles a situation (the structure of the surface) that is analyzed experimentally by any of the techniques mentioned above, using external probes but some of these techniques also involve the motion of electrons througli the surface region this motion in turn is clearly related to the electronic structure of the surface, and so the first-principles calculation and the surface-analysis technique may have and often do have much in common. 

The question of methanol protonation was revisited by Shah et al. (237, 238), who used first-principles calculations to study the adsorption of methanol in chabazite and sodalite. The computational demands of this technique are such that only the most symmetrical zeolite lattices are accessible at present, but this limitation is sure to change in the future. Pseudopotentials were used to model the core electrons, verified by reproduction of the lattice parameter of a-quartz and the gas-phase geometry of methanol. In chabazite, methanol was found to be adsorbed in the 8-ring channel of the structure. The optimized structure corresponds to the ion-paired complex, previously designated as a saddle point on the basis of cluster calculations. No stable minimum was found corresponding to the neutral complex. Shah et al. (237) concluded that any barrier to protonation is more than compensated for by the electrostatic potential within the 8-ring. 

Application of the SCF—Xq—SW method to complex systems containing heavy transition metals bound to one another has been pursued in recent years as a first-principles calculation that seems to provide a basis for discussion of the electronic structures in such cases. 

In the last decade there has been considerable and reasonably satisfactory progress in the understanding of the theoretical aspects of the structural, electronic and optical properties of Si nanostructures. Here we have presented the outcomes of our theoretical study of the properties of Si nanosystems, considering Si nanodots, Si nanowires and Si nanoslabs. We have demonstrated, by first-principle calculations, also beyond the single particle approach, that the structural, electronic, and optical properties of the... 

Theoretical calculations of the electronic structure and optical properties of H-passivated Si quantum wires have been reported by a number of research groups (see, for example, Ref. 116 and references therein). First principles calculations show the same band nesting phenomenon and near-flat dispersion along the T-Z symmetry (wire) direction, as described above for Si quantum wells, and the occurrence of direct gaps.116,117... 

As in the MD method, PES for KMC can be derived from first-principles methods or using empirical energy functionals described above. However, the KMC method requires the accurate evaluation of the PES not only near the local minima, but also for transition regions between them. The corresponding empirical potentials are called reactive, since they can be used to calculate parameters of chemical reactions. The development of reactive potentials is quite a difficult problem, since chemical reactions usually include the breaking or formation of new bonds and a reconfiguration of the electronic structure. At present, a few types of reactive empirical potentials can semi-quantitatively reproduce the results of first-principles calculations these are EAM and MEAM potentials for metals and bond-order potentials (Tersoff and Brenner) for covalent semiconductors and organics. 

The density functional theory of Hohenberg, Kohn and Sham [173,205] has become the standard formalism for first-principles calculations of the electronic structure of extended systems. Kohn and Sham postulate a model state described by a singledeterminant wave function whose electronic density function is identical to the ground-state density of an interacting /V-clcctron system. DFT theory is based on Hohenberg-Kohn theorems, which show that the external potential function v(r) of an //-electron system is determined by its ground-state electron density. The theory can be extended to nonzero temperatures by considering a statistical electron density defined by Fermi-Dirac occupation numbers [241], The theory is also easily extended to the spin-indexed density characteristic of UHF theory and of the two-fluid model of spin-polarized metals [414],... 

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