Methods are derived to simplify and expand the scope of ab initio electronic-structure calculations using relativistic core potentials. The spin-orbit operator obtained at the same level of approximation is expressed in a simpler form to facilitate matrix-element computation. Double-group results are used, when sufficient spatial symmetry is present, both to block the Hamiltonian matrix and to make it real, even though the wave functions are necessarily complex.

This work examines the use of crystal based continuum mechanics in the context of dynamic loading. In particular, we examine model forms and simulations which are relevant to pore collapse in crystalline energetic materials. Strain localization and the associated generation of heat are important for the initiation of chemical reactions in this context. The crystal mechanics based model serves as a convenient testbed for the interactions among wave motion, slip kinetics, defect generation kinetics and physical length scale. After calibration to available molecular dynamics and single crystal gas gun data for HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), the model is used to predict behaviors for the collapse of pores under various conditions. Implications for experimental observations are discussed.

The Cu+ ion impurity in a NaF host has been modeled using a finite cluster of ions to represent the crystal lattice. Several approximations to the lattice potential in the region of the cluster were compared to the exact Madelung potential. The error in the calculated nearest-neighbor distance for the pure host was found to be proportional to the error in the lattice potential. Hartree–Fock calculations were carried out for the ground 1A1g and excited 1,3Eg and 1,3T2g states of the NaF:Cu+ system. The resulting energy level structure was compared to the experimental spectra. The symmetric-stretch potential energy curve, vibrational frequencies, and Franck–Condon factors were calculated for the 1A1g and 1,3T2g states. Using a single configuration coordinate model and a semiempirical spin–orbit coupling scheme, the relative intensities and bandwidths were calculated for absorption to the 1,3T2g states and compared to experiment.

Molecular integral formulas and corresponding computational algorithms are developed for the relativistic spin-orbit and core potential operators that are obtained from atomic relativistic calculations by means of the effective core potential procedure. Much use is made of earlier work on core potential integrals by McMurchie and Davidson. The resulting computer code has been made part of the ARGOS (Argonne, Ohio State) program from the COLUMBUS suite of programs, which computes the needed integrals over symmetry-adapted combinations of generally contacted Gaussian atomic orbitals.

Hartree–Fock cluster calculations have been carried out for the ground 3d10 and excited 3d94s configurations of the Cu+ ion in a NaCl host. Special emphasis has been given to providing an accurate representation of the Coulomb potential due to the remainder of the lattice. Configuration coordinate curves were determined for the symmetric displacement of the nearest-neighbor Cl− ions and are compared to recent Xα calculations. The Hartree–Fock equilibrium Cu–Cl distance was found to be 5.327 bohr, slightly shorter than the calculated nearest-neighbor distance of 5.353 bohr for the pure NaCl host. Comparison of the Hartree–Fock and Xα ground and excited state energies, shows that the Xα approximation reverses the ordering of the 3T2g and 1Eg states, overestimates the equilibrium nearest-neighbor distance, and predicts the a1g vibrational frequency to be about twice the Hartree–Fock value. Using the Franck–Condon factors found with the ab initio potential energy curves, the calculated bandwidths for the 1,3T2g states are found to be in excellent agreement with the low-temperature absorption spectra.

Articles you may be interested inA b i n i t i o effective core potentials including relativistic effects. V. SCF calculations with ω-ω coupling including results for Au2 +, TlH, PbS, and PbSe Relativistic effects in a b i n i t i o effective core potential studies of heavy metal compounds. Application to HgCl2, AuCl, and PtH A b i n i t i o effective core potentials including relativistic effects. IV. Potential energy curves for the ground and several excited states of Au2 A b i n i t i o effective core potentials including relativistic effects. I. Formalism and applications to the Xe and Au atoms Potential energy curves for the ground 1 I.: state of Xe2' the first four states of the Xei ions, and the eight Xe-2 excirner states corresponding to the addition of a 6su g Rydberg electron to these ion cores have been computed using averaged relativistic effective core potentials (AREP) and the self-consistent field approximation for the valence electrons. The calculations were carried out using the LS-coupling scheme with the effects of spin-

We report the results of extensive configuration interaction studies on 16 excited states of water. These states can be accurately described as corresponding to excitation from one of the highest two molecular orbitals (1b1 or 3a1) of the ground state into either the 3s or one of the three 3p Rydberg orbitals. The results provide the most accurate and consistent treatment of these states to date (within 0.1 eV for all known transitions) and form a reliable basis for the assignment of the photon and electron impact spectra of H2O.

Nanoporous silicon has been emerging as a powerful building block for next-generation sensors, catalysts, transistors, and tissue scaffolds. The capability to design novel devices with desired mechanical properties is paramount to their reliability and serviceability. In order to bring further resolution to the highly variable mechanical characteristics of nanoporous silicon, here we perform molecular dynamics simulations to study the effects of ligament thickness, relative density, and pore geometry/orientation on the mechanical properties of nanoporous silicon, thereby determining its Young's modulus, ultimate strength, and toughness as well as the scaling laws versus the features of interior ligaments. Results show that pore shape and pattern dictate stress accumulation inside the designed structure, leading to the corresponding failure signature, such as stretching-dominated, bending-dominated, or stochastic failure signatures, in nanoporous silicon. The nanostructure of the material is also seen to drive or mute size effects such as "smaller is stronger" and "smaller is ductile". This investigation provides useful insight into the behavior of nanoporous silicon and how one might leverage its promising applications.