Local Density Functional Scheme Research Articles

First-principles study of surface phonons on the AlN(1 1 0) surface

Using a linear-response approach based on the pseudo-potential method and the local density functional scheme, we have performed calculations of the atomic and dynamical properties of the (1 1 0) surface of the cubic phase of AlN. Surface localised modes are found with energies below and above the bulk spectrum, as well as in the acoustic–optical and optical–optical gap regions. The first-principles results are compared with results obtained from the application of an empirical adiabatic bond-charge model, providing an assessment of the latter scheme.

Isotopic dependence of the heat capacity of c-C, Si, and Ge: an ab initio calculation

The vibrational spectra of crystalline diamond, silicon, and germanium are calculated with a first-principles local density functional scheme using 64 as well as 128 atoms supercells. The (harmonic) dynamical matrices are obtained from linear response theory. The phonon density of states, calculated for various isotopic masses M, are used to evaluate the vibrational heat capacities C v and their dependence on M at low temperatures. Simple rules obeyed by the isotope effect of C v are discussed. The results are compared with recent experimental data for Ge. It is hoped that this work will encourage and help to interpret analogous measurements in diamond and silicon with different isotopic compositions.

On the gas adsorption effect upon electronic structure of ferromagnetic Co(0 0 0 1)

Effect of C, N or O adsorption on ferromagnetic Co(0 0 0 1) surface on evolution of important electronic features is studied within the local-density functional scheme. At high oxygen or carbon coverage, the spin asymmetry of Co(3d) states at the Fermi level can be reversed; for oxygen, however, the effect is not stable with respect to geometry variation and might correspond to non-equilibrium adatom positions. The concept of exchange splitting for non-homogeneous systems is poorly defined and its presence for well distinguished peaks in the local density of adatom 2p states is expected especially for oxygen. The calculations find, nevertheless, a simple and accurate relation between the spin-splitting of the centre of gravity of 2p electronic sates and value of the magnetic moment induced on adatoms.

First-principles study of structural and dynamical properties of As overlayers on InP( [formula omitted

A first-principles study, using a linear-response approach based on the pseudopotential method and the local density functional scheme, has been carried out for the structural and dynamical properties of As overlayers on InP(1 1 0). Computations have been performed for two structural models: epitaxially continued layer structure and an exchange-reacted structure. For both structural models, we find several characteristic phonon modes in the bulk acoustic-optical gap region. These results have allowed us to provide a critical assessment of the previously reported dynamical properties of this system obtained from the application of a bond charge model.

Vibrational frequencies of diatomic molecules from Car and Parrinello molecular dynamics

The vibrational frequency of selected diatomic molecules (H 2, N 2, F 2, HF, CO) has been calculated from Car-Parrinello molecular dynamics. The associated electronic energies have been obtained within the Born-Oppenheimer approximation by using the local density functional scheme where plane waves and pseudopotentials are used. Our vibrational frequency results, extrapolated to zero effective fictitious mass values, are in good agreement with the experimental values for H 2, N 2, HF and CO, whereas for F 2 our calculated value is larger. The optimized bond lengths and the harmonic vibrational frequencies obtained by a local density functional scheme with plane waves have been compared with other theoretical methods (Hartree-Fock, MP2, CCSD(T), DFT using Gaussian basis sets). There is good agreement between the LDA procedure using plane-wave or Gaussian-type orbital basis sets.

Electronic structure of H adsorbed on Pt13 clusters

Electronic structures of Pt13 clusters and those adsorbed with hydrogen atoms based on the first principles calculations are studied for Pt13 clusters of icosahedral (Ih) symmetry, cuboctahedral (Oh) symmetry and the systems of 8,12,14,20 hydrogen atoms adsorbing to them. Calculations have been done by the self-consistent local density functional scheme using the norm-conserving pseudopotential in the linear combination of the atomic orbital method. The equilibrium distances of Pt–Pt and Pt–H are calculated. The electronic structures of H adsorbed on Pt clusters are turned out to be the shell structure of “the giant atom.” H-1s electrons fill n=1 shell of Pt13H cluster with Pt-6s electrons. The energy levels of shell-2d of naked Pt13 clusters and shell-n=3,4 states of H adsorbed Pt13 clusters, which come from H-1s antibonding are compared with experimental results of in situ x-ray absorption near-edge structure (XANES).

N 2 adsorption around small Ni n ( n=2−4) clusters

The nature of N 2 adsorption and its effect on the geometries, electronic structure and magnetism of Ni n ( n=2−6) clusters has been studied using a linear combination of atomic orbitals-molecular orbital approach within the local density functional scheme. The adsorption sites in small clusters are found to be similar to those on bulk surfaces. The principal effect of N 2 adsorption is a demagnetization upon saturation coverage. The NiNi bonds are dilated but the geometrical structures are left intact. The studies show that the recent chemical methods for determining the geometrical structure of clusters can provide information on structure of bare clusters.

CO and NO chemisorption on heavy metal surfaces: cluster model study

The mechanism for CO or NO strong and weak chemisorptions on tungsten and platinum surfaces is discussed by the cluster model for metal surfaces on the basis of the local density functional scheme using the norm-conserving pseudo-potential in the linear combination of atomic orbitals method. Total energies, stretching frequencies and electronic structures of adsorbed CO and NO molecules obtained by the self-consistent calculations provide us with information to understand the experimental phenomena quantitatively.

Metal clusters as giant atoms

M12X-type metal clusters of icosahedral symmetry are discussed in terms of the giant atom concept on the basis of the electronic shell structures in free-electron-like metal clusters. The first-principles calculations for Au12,13, Ag12,13, Al12,13, Au12Cr, and Al12Si clusters have been done by the self-consistent local density functional scheme using the norm-conserving pseudopotential in the linear combination of atomic orbitals method. Electronic shell structures in icosahedral clusters are formed by 6s, 5s and 3p orbitals or peripheral atoms in Au, Ag, and Al clusters, respectively. By doping Cr into Au12 and Si into Al12 clusters M13 clusters are stabilized by about 0.7 eV atom-1 (Au12Cr) and 0.2 eV atom-1 (Al12Si) because of the closed shell formation. Interactions between clusters, cluster and surface, and cluster and metal tip used in the atomic force microscope are discussed based on the Harris functional scheme. Dimers of Au12Cr and Al12Si are weakly bound, and the Au13 cluster on Si(111) has two kinds of binding, but Al13 does not. The repulsive or attractive nature of the force between the cluster and Pt tip is considerably dependent on the cluster-tip distance.

Geometry optimization of molecules within anLCGTO local-density functional approach

We describe our implementation of geometry optimization techniques within the linear combination of Gaussian-type orbitals (LCGTO) approach to local-density functional theory. The algorithm for geometry optimization is based on the evaluation of the gradient of the total energy with respect to internal coordinates within the local-density functional scheme. We present optimization results for a range of small molecules which serve as test cases for our approach.

Self-Consistent Band Structures of First-Stage Alkali-Metal Graphite Intercalation Compounds

Mechanisms of charge transfer along c -axis in first stage alkali-metal graphite intercalation compounds are studied by the self-consistent numerical-basis-set LCAO band-structure calculations within the local density functional scheme. An augmented LCAO basis set consisting of localized orbitals located at the interstitial sites between graphite layers in addition to the optimized atomic orbitals situated at the atomic sites, successfully describes interlayer states of pristine graphite. Moreover, in the cases of C 8 K, C 8 Rb and C 8 Cs, it is found that both the s -states originating from alkali-atoms and the interlayer states are located above the Fermi level. However, Mulliken charge population analysis for C 8 Cs indicates that a small amount of charge remains in 6 s -orbital of Cs due to the hybridization between the 6 s -orbital and the occupied graphite bands.

Comparison of local density functional Hartree-Fock and configuration interaction in the STO-3G orbital basis for some first-row diatomics

The local density functional (LDF) scheme has been implemented in Gaussian orbital basis sets by modifying GAUSSIAN70. Calculations for H2, Li2, N2 and F2 with the STO-3G basis set show that the LDF scheme is generally better than Hartree-Fock in reproducing bond lengths and vibration frequencies, and is comparable with configuration interaction (CI) in the same basis. Energy changes in the valence electrons are, however, better described with LDF than with CI. STO-3G results for fourteen closed-shell atoms and ions in the LDF scheme are also given.

Many-body effects in the photoemission from adsorbates

The changes in the density of states due to hydrogen atoms adsorbed on a jellium and a W[100] surface are calculated. Special emphasis is given to a subdivision into adsorbate and substrate effects as well as to many-body corrections. The scheme is based on work of Hubbard and of Brenig and Schonhammer and is developed in such a way that electron-electron interactions in the substrate can be treated within an effective potential approach, for example, the local density functional scheme.