D. A. Papaconstantopoulos

Applications of a tight-binding total-energy method for transition and noble metals: Elastic constants, vacancies, and surfaces of monatomic metals

A recent tight-binding scheme provides a method for extending the results of first principles calculations to regimes involving

Electronic structure calculations of lead chalcogenides PbS, PbSe, PbTe

10^2 - 10^3

Electronic structure and magnetism of complex materials

atoms in a unit cell. The method uses an analytic set of two-center, non-orthogonal tight-binding parameters, on-site terms which change with the local environment, and no pair potential. The free parameters in this method are chosen to simultaneously fit band structures and total energies from a set of first-principles calculations for monatomic fcc and bcc crystals. To check the accuracy of this method we evaluate structural energy differences, elastic constants, vacancy formation energies, and surface energies, comparing to first-principles calculations and experiment. In most cases there is good agreement between this theory and experiment. We present a detailed account of the method, a complete set of tight-binding parameters, and results for twenty-nine of the alkaline earth, transition and noble metals.

Dynamical properties of Au from tight-binding molecular-dynamics simulations

In this work, we have extended our study of the mechanical properties and the electronic structure of PbTe to include other Pb chalcogenide compounds (PbSe, PbS). The calculations were performed self-consistently using the scalar-relativistic full-potential linearized augmented plane wave method. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) to density-functional theory were applied. The equilibrium lattice constants and the bulk modulus of a number of structures (NaCl, CsCl, ZnS) were calculated as well as the elastic constants for the structures (NaCl, CsCl). The NaCl structure is found to be the most stable one among all the three phases considered. We have found that the GGA predicts the elastic constants in good agreement with experimental data. Both the LDA and GGA were successful in predicting the location of the band gap at the L point of the Brillouin zone but they are inconclusive regarding the value of the band-gap width. To resolve the issue of the gap, we performed Slater–Koster (SK) tight-binding calculations, including the spin–orbit coupling in the SK Hamiltonian. The SK results that are based on our GGA calculations give the best agreement with experiment. Results are reported for the pressure dependence of the energy gap of these compounds in the NaCl structure. The pressure variation of the energy gap indicates a transition to a metallic phase at high pressure. Band structure calculations in the CsCl structure show a metallic state for all compounds. The electronic band structure in the ZnS phase shows an indirect band gap at the W and X point of the Brillouin zone.

Insights into the fracture mechanisms and strength of amorphous and nanocomposite carbon.

1 Low-Lying Magnetic Excitations in Itinerant Systems: SDFT Calculations.- 2 Calculation of Magneto-crystalline Anisotropy in Transition Metals.- 3 Electronic Structure and Magnetism of Correlated Systems: Beyond LDA.- 4 Ferromagnetism in (III,Mn)V Semiconductors.- 5 Noncollinear Magnetism in Systems with Relativistic Interactions.- 6 Orbital Degeneracy and Magnetism of Perovskite Manganese Oxides.- 7 Magnetism in Ruthenates.

Theoretical prediction of MoN as a high Tc superconductor

We studied the dynamical properties of Au using our previously developed tight-binding method. Phonon-dispersion and density-of-states curves at T=0 K were determined by computing the dynamical-matrix using a supercell approach. In addition, we performed molecular-dynamics simulations at various temperatures to obtain the temperature dependence of the lattice constant and of the atomic mean-square-displacement, as well as the phonon density-of-states and phonon-dispersion curves at finite temperature. We further tested the transferability of the model to different atomic environments by simulating liquid gold. Whenever possible we compared these results to experimental values.

Second-moment interatomic potential for Cu-Au alloys based on total-energy calculations and its application to molecular-dynamics simulations

Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs intergrain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.

Ab initio based tight-binding molecular dynamics simulation of the sticking and scattering of O2∕Pt(111)

Abstract A re-examination of several recent band structure calculations for transition metal compounds has suggested that Mo-based B1 structure compounds should be good superconductors. Using augmented-plane-wave band calculations and the Gaspari-Gyorffy approach for the electron-phonon interaction, we predict that MoC and MoN should have significantly higher Tc than their Nb-based counterparts NbC (Tc=11K) and NbN (Tc=17K).

Electronic structure calculations of PbTe

We have evaluated interatomic potentials of Cu, Au and Cu-Au ordered alloys in the framework of the second-moment approximation to the tight-binding theory by fitting to the volume dependence of the total energy of these materials computed by first-principles augmented-plane-wave calculations. We have applied this scheme to calculate the bulk modulus and elastic constants of the pure elements and alloys and we have obtained a good agreement with experiment. We also have performed molecular-dynamics simulations at various temperatures, deducing the temperature dependence of the lattice constants and the atomic mean square displacements, as well as the phonon density of states and the phonon-dispersion curves of the ordered alloys. A satisfactory accuracy was obtained, comparable to previous works based on the same approximation, but resulting from fitting to various experimental quantities.

Second-moment interatomic potential for Al, Ni and Ni–Al alloys, and molecular dynamics application

The sticking and scattering of O(2)Pt(111) has been studied by tight-binding molecular dynamics simulations based on an ab initio potential energy surface. We focus, in particular, on the sticking probability as a function of the angle of incidence and the energy and angular distributions in scattering. Our simulations provide an explanation for the seemingly paradox experimental findings that adsorption experiments suggest that the O(2)Pt(111) interaction potential should be strongly corrugated while scattering experiments indicate a rather small corrugation. The potential energy surface is indeed strongly corrugated which leads to a pronounced dependence of the sticking probability on the angle of incidence. The scattered O(2) molecules, however, experience a rather flat surface due to the fact that they are predominantly scattered at the repulsive tail of the potential.